tcp: Remove v6 flag from tcp_epoll_ref

This bit in the TCP specific epoll reference indicates whether the
connection is IPv6 or IPv4.  However the sites which refer to it are
already calling accept() which (optionally) returns an address for the
remote end of the connection.  We can use the sa_family field in that
address to determine the connection type independent of the epoll
reference.

This does have a cost: for the spliced case, it means we now need to get
that address from accept() which introduces an extran copy_to_user().
However, in future we want to allow handling IPv4 connectons through IPv6
sockets, which means we won't be able to determine the IP version at the
time we create the listening socket and epoll reference.  So, at some point
we'll have to pay this cost anyway.

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

tcp.h

@@ -33,7 +33,6 @@ void tcp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
  * union tcp_epoll_ref - epoll reference portion for TCP connections
  * @listen:		Set if this file descriptor is a listening socket
  * @outbound:		Listening socket maps to outbound, spliced connection
- * @v6:			Set for IPv6 sockets or connections
  * @timer:		Reference is a timerfd descriptor for connection
  * @index:		Index of connection in table, or port for bound sockets
  * @u32:		Opaque u32 value of reference
@@ -42,7 +41,6 @@ union tcp_epoll_ref {
 	struct {
 		uint32_t	listen:1,
 				outbound:1,
-				v6:1,
 				timer:1,
 				index:20;
 	} tcp;