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: syzbot+8151ef969c170f76706b@syzkaller.appspotmail.com
Reported by: syzbot+eb679adb3304c511c1e4@syzkaller.appspotmail.com
Reviewed by: markj, rrs
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D32983