conntrack: Fix icmp error address sanity check.

conntrack: Fix icmp error address sanity check.

An address sanity check is done on icmp error packets to
check that the icmp error payload makes sense w.r.t. the
packet itself.

The sanity check was partially incorrect since it tried
to verify the source address of the error packet against the
original destination, which does not makes since the error
can be generated by any intermediate node.

Reported-by: wangzhike <wangzhike@jd.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2017-December/341609.html
Fixes: a489b1685 ("conntrack: New userspace connection tracker.")
CC: Daniele Di Proietto <diproiettod@vmware.com>
Signed-off-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: wangzhike <wangzhike@jd.com>
Co-authored-by: wangzhike <wangzhike@jd.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>