Leaf 'Egress' of 'transmit-packet' rpc is not required

Hello,

the leaf 'egress' of the 'transmit-packet' rpc of the packet-processing service was used in order to define the output action (i.e. how the packet should be processed by a switch) of a packet-out event. Therefore, it is a mandatory field in cases someone uses this rpc.

However, you can also define the output action by using the action list of the aforementioned rpc since the bug regarding the fact that ODL was ignoring this list is fixed (https://git.opendaylight.org/gerrit/#/c/28195/).

Therefore, it exists a duplication of actions since the ODL forces a programmer to define the egress leaf. This may cause redundant actions to be perfomerd when a switch processes a packet out event.

I suggest removing this leaf from the yang model and the imlementation as well. In this way, a programmer can use only the action list in order to define an output action.