Keep all of tunnel metadata in flow.

Keep all of tunnel metadata in flow.

Do not clear tunnel metadata on tunnel input.

This is a backport of 4110a57 (Keep all of tunnel metadata in
flow.) to branch-1.11.  This fixes an issue with received tunnel
traffic and megaflows.  xlate_actions() calls tnl_port_should_receive()
to determine whether it should un-wildcard the tunnel fields.  Without
this commit, the original flow's tunnel information is zeroed and is
unavailable for tnl_port_should_receive()'s use to determine whether
it's a tunnel flow or not.  This resulted in some tunnel traffic
being wildcarded inappropriately.

Bug #18277.

Signed-off-by: Justin Pettit <jpettit@nicira.com>
Signed-off-by: Jarno Rajahalme <jarno.rajahalme@nsn.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>