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>
diff --git a/include/net/af_rxrpc.h b/include/net/af_rxrpc.h
index 7b0f886..f9224e8 100644
--- a/include/net/af_rxrpc.h
+++ b/include/net/af_rxrpc.h
@@ -49,5 +49,7 @@
 void rxrpc_kernel_free_skb(struct sk_buff *);
 struct rxrpc_call *rxrpc_kernel_accept_call(struct socket *, unsigned long);
 int rxrpc_kernel_reject_call(struct socket *);
+void rxrpc_kernel_get_peer(struct socket *, struct rxrpc_call *,
+			   struct sockaddr_rxrpc *);
 
 #endif /* _NET_RXRPC_H */