inet: fix IP(V6)_RECVORIGDSTADDR for udp sockets

inet: fix IP(V6)_RECVORIGDSTADDR for udp sockets

[ Upstream commit 39b2dd765e0711e1efd1d1df089473a8dd93ad48 ]

Socket cmsg IP(V6)_RECVORIGDSTADDR checks that port range lies within
the packet. For sockets that have transport headers pulled, transport
offset can be negative. Use signed comparison to avoid overflow.

Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
Reported-by: Nisar Jagabar <njagabar@cloudmark.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>