ice: support RFC 6544 ICE over TCP

This patch is the first one used to perform ICE over TCP. Leads to
major changes:

+ IceTransport has now a tcpEnable parameters to use TCP instead
of UDP. Also, this patch makes ICE aggressive nomination available.
+ File transfer is now usable without TURN in a local network. For
now, UPnP is not supported, this will come in a near future. Now,
it can use a direct connection between two pairs.

If the negotiation between peer fails, the TURN is used as a
fallback. Moreover, to avoid breaking compability when a peer wants
to connect, it will send the SDP message followed by TURN ips (like
the current version).

Change-Id: I0425c7da34ff2bc272c376261847195be768d522