Merge branch 'pmtu-selftest-fixes'

Paolo Abeni says:

====================
selftests: pmtu: fix and increase coverage

This series includes a fixup for the pmtu.sh test script, related to IPv6
address management, and adds coverage for the recently reported and fixed
PMTU exception issue

v2 -> v3:
 - more cleanups

v1 -> v2:
 - several script cleanups
====================

Signed-off-by: David S. Miller <davem@davemloft.net>