tests/ofproto-dpif - fragment handling: Add detail.

Add transport port modifications to the existing frags handling test
case.

This demonstrates incorrect behavior by not moving the destination
port number to source port in normal mode for first fragment, as the
transport port numbers have been zeroed and the move has no effect,
and by allowing moves to/from transport ports on later fragments
(which do not have a transport header).

Next patches fix these problems.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
ofproto-dpif-xlate: Do not clear ports with frags in xlate_actions().

Transport ports are already cleared for lookup if need be, and they
should be available for action processing, so do not clear them in
xlate_actions().

A drop flow takes care of dropping the packet, so no special case is
needed in xlate_actions().

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