net/enic: fix flow action reordering

net/enic: fix flow action reordering

The current implementation produces wrong ordering for several cases
like these:

1. mark, decap, steer
Current: steer, mark, decap
Correct: mark, steer, decap

2. decap, steer, steer
Current: steer, steer, decap
Correct: steer, decap, steer

Simplify the logic and swap 1st steer and decap.
Also, allow just one decap action per flow.

Fixes: ea7768b5bba8 ("net/enic: add flow implementation based on Flow Manager API")
Cc: stable@dpdk.org
Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
Signed-off-by: John Daley <johndale@cisco.com>