Fix potential bug in handling metadata.

In a OFPIT_WRITE_METADATA the value would be reset, as pointed
by Jean Tourrilhes.
This commit fix this behavior and also add tunnel metadata information
to the packet parsing.
Fix IPv4 checksum on IPv4 ECN or DSCP set field

This commit updates the IPv4 packet checksum after changing the DSCP
or ECN fields. Furthermore, it add the case of setting IPv6 DSCP and ECN.
Always clone packet with an empty action-set.

Fix a bug where if an action-list invoke a group, the current action-set
leaks into the execution of the group bucket.
Break long string in flow stat reply for readability.
Fix a double free in group of type all with new packet freeing strategy.
Add TUNNEL_ID to set_field action.

Implements the the tunnel id set_field action, enabling
matching on this field after the action.
Also fix a little bug when checking if the tunnel_id field value
already exists.
Fix OXM_SCTP_DST print
Fix malloc being called twice on reply_port and reply_queue unpack messages
Change tunnel_id from network to host byte order.

Without these changes, flows were being added incorrectly.