Clarify tunnel wildcarding.

It would seem we should set the 'tunnel.ip_dst' in 'wc' when calling
tnl_port_should_receive(), as it is reading that flow field.  However,
since tunnels' datapath port numbers are different from the non-tunnel
ports, and we always unwildcard the 'in_port', we do not need to
unwildcard the 'tunnel.ip_dst' for non-tunneled packets.

Also, 'nw_tos' need not be unwildcarded if it is not examined.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>