Its two calls to evbuffer_peek() used 3.5% of CPU use (measured with perf
when built with RelWithDebInfo). I added vecs() so that libtransmsision
could send noncontiguous buffers via utp_writev(); but in my testing, all
the buffers being sent are contiguous and so this is unnecessary work.
* refactor: make tr_peer_socket.type private
* refactor: reimplement tr_peerIo::address() as a wrapper around tr_peer_socket::address()
* refactor: remove tr_address, tr_port from tr_peerIo
* refactor: replace tr_netClosePeerSocket() with tr_peer_socket::close()
