Cannot open MMS data connection with Saunalahti SIM

Test steps (on mako HW, image 157):
 - Insert Saunalahti (Finland) prepaid SIM
 - Check that the MMS access point settings are correctly provisioned (apn=mms, proxy=213.161.41.57, mmsc=http://mms.elisa.fi)
 - Send or receive an MMS
Actual result:
 - Neither sending nor receiving MMS succeeds
 - oFono cannot open the data connection for MMS, because the GPRS context returned by the modem does not include DNS details:

Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: < 00 00 00 00 de 00 00 00 00 00 00 00 09 00 00 00 ................
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 01 00 00 00 00 00 00 00 ff ff ff ff 02 00 00 00 ................
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 02 00 00 00 02 00 00 00 49 00 50 00 00 00 00 00 ........I.P.....
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 0a 00 00 00 72 00 6d 00 6e 00 65 00 74 00 5f 00 ....r.m.n.e.t._.
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 75 00 73 00 62 00 30 00 00 00 00 00 10 00 00 00 u.s.b.0.........
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 31 00 30 00 2e 00 31 00 37 00 30 00 2e 00 34 00 1.0...1.7.0...4.
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 38 00 2e 00 31 00 35 00 32 00 2f 00 33 00 30 00 8...1.5.2./.3.0.
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 00 00 00 00 00 00 00 00 00 00 00 00 0d 00 00 00 ................
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 31 00 30 00 2e 00 31 00 37 00 30 00 2e 00 34 00 1.0...1.7.0...4.
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: Device: 38 00 2e 00 31 00 35 00 33 00 00 00 8...1.5.3...
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: gril/gril.c:handle_response() comparing req->id: 222 to message->serial_no: 222
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: drivers/rilmodem/gprs-context.c:ril_setup_data_call_cb() *gc: 0x6b69c8
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: gril/grilunsol.c:g_ril_unsol_parse_data_call_list()
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: handle_settings: no DNS:
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: drivers/rilmodem/gprs-context.c:ril_gprs_context_deactivate_primary() *gc: 0x6b69c8 cid: 0 active_rild_cid: -1
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: ril_gprs_context_deactivate_primary: couldn't remove call_list listener for apn: mms.
Jul 28 14:18:25 ubuntu-phablet ofonod[1254]: gril/gril.c:ril_request_create() req: RIL_REQUEST_DEACTIVATE_DATA_CALL, id: 223, data_len: 24