epoll: Split handling of listening TCP sockets into their own handler

tcp_sock_handler() handles both listening TCP sockets, and connected TCP
sockets, but what it needs to do in those cases has essentially nothing in
common.  Therefore, give listening sockets their own epoll_type value and
dispatch directly to their own handler from the top level.  Furthermore,
the two handlers need essentially entirely different information from the
reference: we re-(ab)used the index field in the tcp_epoll_ref to indicate
the port for the listening socket, but that's not the same meaning.  So,
switch listening sockets to their own reference type which we can lay out
as we please.  That lets us remove the listen and outbound fields from the
normal (connected) tcp_epoll_ref, reducing it to just the connection table
index.

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

tcp_splice.h

@@ -10,7 +10,7 @@ struct tcp_splice_conn;
 
 void tcp_splice_sock_handler(struct ctx *c, struct tcp_splice_conn *conn,
 			     int s, uint32_t events);
-bool tcp_splice_conn_from_sock(struct ctx *c, union epoll_ref ref,
+bool tcp_splice_conn_from_sock(struct ctx *c, union tcp_listen_epoll_ref ref,
 			       struct tcp_splice_conn *conn, int s,
 			       const struct sockaddr *sa);
 void tcp_splice_init(struct ctx *c);