tcp, tcp_splice: Avoid double layered dispatch for connected TCP sockets

Currently connected TCP sockets have the same epoll type, whether they're
for a "tap" connection or a spliced connection.  This means that
tcp_sock_handler() has to do a secondary check on the type of the
connection to call the right function.  We can avoid this by adding a new
epoll type and dispatching directly to the right thing.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

passt.h

@@ -51,6 +51,8 @@ enum epoll_type {
 	EPOLL_TYPE_NONE = 0,
 	/* Connected TCP sockets */
 	EPOLL_TYPE_TCP,
+	/* Connected TCP sockets (spliced) */
+	EPOLL_TYPE_TCP_SPLICE,
 	/* Listening TCP sockets */
 	EPOLL_TYPE_TCP_LISTEN,
 	/* timerfds used for TCP timers */