Add support for requesting the fd again to rebind to the next interface.

This not done via android_control since calling management from management leads to an infinitive loop
Remove #ifdefs for client nat support.

The client-nat feature was always unconditionally enabled
Don’t redirect the gateway on Android even if requested

Routing loops are avoided using the VPNService API
Fix routing when not being able to read /proc/route
Peer-id patch

Added new packet format P_DATA_V2, which includes peer-id. If server
supports, client sends all data packets in the new format. When data
packet arrives, server identifies peer by peer-id. If peer's ip/port has
changed, server assumes that client has floated, verifies HMAC and
updates ip/port in internal structs.