Previously TransportFactory interface was responsible for creation
and initialization of several protocol layers, including PseudoTCP and
authentication (TLS). Simplified it so now it only creates raw datagram
transport channel. PseudoTcpChannelFactory is now responsible for
setting up PseudoTcpAdapter and AuthenticatingChannelFactory takes care
of channel authentication. Also added DatagramChannelFactory for
Datagram channels.

This change will make it possible to replace PseudoTcpChannelFactory
with an object that creates SCTP-based channels.

Also fixed a bug in SslHmacChannelAuthenticator. It wasn't working
properly when deleted from the callback. (base::Callback objects
shouldn't be deleted while being called because when deleted they
also destroy reference parameters values they are holding).

BUG=402993

Review URL: https://codereview.chromium.org/551173004

Cr-Commit-Position: refs/heads/master@{#294653}