ipv6: fix leaking uninitialized port number of offender sockaddr

[ Upstream commit 1fa4c710b6fe7b0aac9907240291b6fe6aafc3b8 ]

Offenders don't have port numbers, so set it to 0.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>