ran_peer: Move rx_reset_ack logic into its own func

Later on we want to do extra steps upon receiving a Rx Reset Ack
(checking for Osmux support from peer). Let's move handling of this
message into its own function to have handling implementation in one
place.

Change-Id: I516c4baf6071d26f6c530726d93677bed968efd1
1 file changed