rxrpc: Provide a way for AFS to ask for the peer address of a call

Provide a function so that kernel users, such as AFS, can ask for the peer
address of a call:

   void rxrpc_kernel_get_peer(struct rxrpc_call *call,
			      struct sockaddr_rxrpc *_srx);

In the future the kernel service won't get sk_buffs to look inside.
Further, this allows us to hide any canonicalisation inside AF_RXRPC for
when IPv6 support is added.

Also propagate this through to afs_find_server() and issue a warning if we
can't handle the address family yet.

Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/server.c

@@ -178,13 +178,18 @@ server_in_two_cells:
 /*
  * look up a server by its IP address
  */
-struct afs_server *afs_find_server(const struct in_addr *_addr)
+struct afs_server *afs_find_server(const struct sockaddr_rxrpc *srx)
 {
 	struct afs_server *server = NULL;
 	struct rb_node *p;
-	struct in_addr addr = *_addr;
+	struct in_addr addr = srx->transport.sin.sin_addr;
 
-	_enter("%pI4", &addr.s_addr);
+	_enter("{%d,%pI4}", srx->transport.family, &addr.s_addr);
+
+	if (srx->transport.family != AF_INET) {
+		WARN(true, "AFS does not yes support non-IPv4 addresses\n");
+		return NULL;
+	}
 
 	read_lock(&afs_servers_lock);