ospfd CI crash w/ assertion failure

[eqvinox]

*** defaultIntf: warning: r1 has no interfaces
*** defaultIntf: warning: lm has no interfaces

r2: ospfd crashed. Core file found - Backtrace follows:
[New LWP 29756]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `/usr/lib/frr/ospfd'.
Program terminated with signal SIGABRT, Aborted.
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007fc0c6875801 in __GI_abort () at abort.c:79
#2  0x00007fc0c686539a in __assert_fail_base (fmt=0x7fc0c69ec7d8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x55ac3aea2a93 "node", file=file@entry=0x55ac3aea2a53 "ospfd/ospf_packet.c", line=line@entry=666, function=function@entry=0x55ac3aea4f88 "ospf_write") at assert.c:92
#3  0x00007fc0c6865412 in __GI___assert_fail (assertion=0x55ac3aea2a93 "node", file=0x55ac3aea2a53 "ospfd/ospf_packet.c", line=666, function=0x55ac3aea4f88 "ospf_write") at assert.c:101
#4  0x000055ac3ae5a174 in ?? ()
#5  0x00007fc0c72cb076 in thread_call () from /usr/lib/x86_64-linux-gnu/frr/libfrr.so.0
#6  0x00007fc0c729cc68 in frr_run () from /usr/lib/x86_64-linux-gnu/frr/libfrr.so.0
#7  0x000055ac3ae43195 in main ()
2019-06-17 17:35:08,620 ERROR: assert failed at "test_ospf_sr_topo1/test_memory_leak": 
r2: ospfd crashed. Core file found - Backtrace follows:
[New LWP 29756]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `/usr/lib/frr/ospfd'.
Program terminated with signal SIGABRT, Aborted.
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007fc0c6875801 in __GI_abort () at abort.c:79
#2  0x00007fc0c686539a in __assert_fail_base (fmt=0x7fc0c69ec7d8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x55ac3aea2a93 "node", file=file@entry=0x55ac3aea2a53 "ospfd/ospf_packet.c", line=line@entry=666, function=function@entry=0x55ac3aea4f88 "ospf_write") at assert.c:92
#3  0x00007fc0c6865412 in __GI___assert_fail (assertion=0x55ac3aea2a93 "node", file=0x55ac3aea2a53 "ospfd/ospf_packet.c", line=666, function=0x55ac3aea4f88 "ospf_write") at assert.c:101
#4  0x000055ac3ae5a174 in ?? ()
#5  0x00007fc0c72cb076 in thread_call () from /usr/lib/x86_64-linux-gnu/frr/libfrr.so.0
#6  0x00007fc0c729cc68 in frr_run () from /usr/lib/x86_64-linux-gnu/frr/libfrr.so.0
#7  0x000055ac3ae43195 in main ()

seen on #4528 (unrelated PR), seems to happen extremely rarely at random...

[rwestphal]

Probably related to #4248.