tcp: Fix a locking issue related to logging
tcp_respond() is sometimes called with only a read lock.
The logging however, requires a write lock. So either
try to upgrade the lock if needed, or don't log the packet.
Reported by: firstname.lastname@example.org
Reported by: email@example.com
Reviewed by: markj, rrs
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D32983