Add P2PDatagramSocket and P2PStreamSocket interfaces.

Add P2PDatagramSocket and P2PStreamSocket interfaces.

Previously remoting code was using net::Socket and net::StreamSocket
for datagram and stream socket. Problem is that net::StreamSocket
interface contains a lot of methods that are not relevant for
peer-to-peer connections in remoting. Added P2PDatagramSocket and
P2PStreamSocket interfaces independent of net::Socket. This allowed to
remove a lot of the redundant code needed for net::StreamSocket
implementations. There are two new adapters required in
SslHmacChannelAuthenticator for the SSL layer, but these won't be
necessary after we migrate to QUIC.

Review URL: https://codereview.chromium.org/1197853003

Cr-Commit-Position: refs/heads/master@{#339489}