In udp_input() when walking the pcblist we can come across
an inp marked FREED after the epoch(9) changes.
Check once we hold the lock and skip the inp if it is the case.
Contrary to IPv6 the locking of the inp outside the multicast
section and hence a single check seems to suffice. Harmonization
should happen at some point but currently keep the code changes
to a minimum before stable/12 happens.
PR: 232192