Merge branch 'udp-a-few-fixes'

Paolo Abeni says:

====================
udp: a few fixes

This series includes some UDP-related fixlet. All this stuff has been
pointed out by the sparse tool. The first two patches are just annotation
related, while the last 2 cover some very unlikely races.
====================

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