SUNRPC: TCP/UDP always close the old socket before reconnecting

It is not safe to call xs_reset_transport() from inside xs_udp_setup_socket()
or xs_tcp_setup_socket(), since they do not own the correct locks. Instead,
do it in xs_connect().

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>