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/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index 14d04c8..a191675 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -16,7 +16,7 @@
 #include "internal.h"
 #include "afs_cm.h"
 
-static struct socket *afs_socket; /* my RxRPC socket */
+struct socket *afs_socket; /* my RxRPC socket */
 static struct workqueue_struct *afs_async_calls;
 static atomic_t afs_outstanding_calls;
 static atomic_t afs_outstanding_skbs;