Peer-id patch v7

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.

Changes in v7:
A few nitpicks.

Changes in v6:
Fixed: Make sure float won't happen if hmac check failed (regression).
Fixed: Access outside of bounds of array, which has caused memory
corruption and crash.
Various review fixes.

Changes in v5:
Protection agains replay attack by commiting float changes only after
existing packet processing flow has completed.

If peer floats to an address which is already taken by another active
session, drop float packet, otherwise disconnect existing session.

Changes in v4:
Handles correctly float to an address which is used by another peer.
This also has fixed crash on assert in multi_client_disconnect.

Changes in v3:
Bugfix: If float happens after TLS renegotiation and there are no
data packets between reneg and float, server will not recognize floated
client.
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1416755831-21250-1-git-send-email-lstipakov@gmail.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9270

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Add google break pad support (only tested under Android)
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
Use pseudo gw as default gw on Android as a workaround for not being able to read /proc/net/route