odp-util: Commit ICMP set only for ICMP packets.

odp-util: Commit ICMP set only for ICMP packets.

commit_set_icmp_action() should do its job only if the packet is ICMP,
otherwise there will be two problems:

* A set ICMP action will be inserted in the ODP actions and the flow
  will be slow pathed.
* The tp_src and tp_dst field will be unwildcarded.

Normal TCP or UDP packets won't be impacted, because
commit_set_icmp_action() is called after commit_set_port_action() and it
will see the fields as already committed (TCP/UCP transport ports and ICMP
code/type are stored in the same members in struct flow).

MPLS packets though will hit the bug, causing a nonsensical set action
(which will end up zeroing the transport source port) and an invalid
mask to be generated.

The commit also alters an MPLS testcase to trigger the bug.