Changes

gtpc2: allow to set the restart counter

The restart counter a 8 bit value is used to detect if a component
has been restarted.
By the spec the IE recovery should be only present in the first PDU
towards a new peer.
But this is for a later improvement.
Use system_time by millisecond mod 256 as default.
Further allow the supervisor to set it to a specific value.

Change-Id: I1e894a2c54dd180c0bc3a6f78d0bb7dd455cad81