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

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>