ipv4: enable route flushing in network namespaces

Relevant upstream commit is:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5cdda5f1d6adde02da591ca2196f20289977dc56

See
https://lists.ubuntu.com/archives/kernel-team/2019-September/103670.html

https://lists.ubuntu.com/archives/kernel-team/2019-September/103672.html

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-disco' to 'verification-done-disco'. If the problem still exists, change the tag 'verification-needed-disco' to 'verification-failed-disco'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

This bug was fixed in the package linux - 5.0.0-32.34

---------------
linux (5.0.0-32.34) disco; urgency=medium

  * disco/linux: 5.0.0-32.34 -proposed tracker (LP: #1846097)

  * CVE-2019-14814 // CVE-2019-14815 // CVE-2019-14816
    - mwifiex: Fix three heap overflow at parsing element in cfg80211_ap_settings

  * CVE-2019-15505
    - media: technisat-usb2: break out of loop at end of buffer

  * CVE-2019-2181
    - binder: check for overflow when alloc for security context

  * Support Hi1620 zip hw accelerator (LP: #1845355)
    - [Config] Enable HiSilicon QM/ZIP as modules
    - crypto: hisilicon - add queue management driver for HiSilicon QM module
    - crypto: hisilicon - add hardware SGL support
    - crypto: hisilicon - add HiSilicon ZIP accelerator support
    - crypto: hisilicon - add SRIOV support for ZIP
    - Documentation: Add debugfs doc for hisi_zip
    - crypto: hisilicon - add debugfs for ZIP and QM
    - MAINTAINERS: add maintainer for HiSilicon QM and ZIP controller driver
    - crypto: hisilicon - fix kbuild warnings
    - crypto: hisilicon - add dependency for CRYPTO_DEV_HISI_ZIP
    - crypto: hisilicon - init curr_sgl_dma to fix compile warning
    - crypto: hisilicon - add missing single_release
    - crypto: hisilicon - fix error handle in hisi_zip_create_req_q
    - crypto: hisilicon - Fix warning on printing %p with dma_addr_t
    - crypto: hisilicon - Fix return value check in hisi_zip_acompress()
    - crypto: hisilicon - avoid unused function warning

  * xfrm interface: several kernel panic (LP: #1836261)
    - xfrm interface: fix memory leak on creation
    - xfrm interface: avoid corruption on changelink
    - xfrm interface: ifname may be wrong in logs
    - xfrm interface: fix list corruption for x-netns
    - xfrm interface: fix management of phydev

  * shiftfs: drop entries from cache on unlink (LP: #1841977)
    - SAUCE: shiftfs: fix buggy unlink logic

  * shiftfs: mark kmem_cache as reclaimable (LP: #1842059)
    - SAUCE: shiftfs: mark slab objects SLAB_RECLAIM_ACCOUNT

  * Suspend to RAM(S3) does not wake up for latest megaraid and mpt3sas
    adapters(SAS3.5 onwards) (LP: #1838751)
    - PCI: Restore Resizable BAR size bits correctly for 1MB BARs

  * No sound inputs from the external microphone and headset on a Dell machine
    (LP: #1842265)
    - ALSA: hda - Expand pin_match function to match upcoming new tbls
    - ALSA: hda - Define a fallback_pin_fixup_tbl for alc269 family

  * Add -fcf-protection=none when using retpoline flags (LP: #1843291)
    - SAUCE: kbuild: add -fcf-protection=none when using retpoline flags

  * Disco update: upstream stable patchset 2019-09-25 (LP: #1845390)
    - bridge/mdb: remove wrong use of NLM_F_MULTI
    - cdc_ether: fix rndis support for Mediatek based smartphones
    - ipv6: Fix the link time qualifier of 'ping_v6_proc_exit_net()'
    - isdn/capi: check message length in capi_write()
    - ixgbe: Fix secpath usage for IPsec TX offload.
    - net: Fix null de-reference of device refcount
    - net: gso: Fix skb_segment splat when splitting gso_size mangled skb having
      linear-headed frag_list
    - net: phylink: Fix flow control resolution
    - net: s...

All autopkgtests for the newly accepted linux-bluefield (5.0.0-1003.12) for bionic have finished running.
The following regressions have been reported in tests triggered by the package:

fsprotect/unknown (armhf)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/bionic/update_excuses.html#linux-bluefield

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!