afs: Use a dynamic port if 7001 is in use

It is not required that the afs client operate on port 7001.
The port could be in use because another kernel or userspace
client has already bound to it.

If the port is in use, just fallback to using a dynamic port.
Signed-off-by: NMarc Dionne <marc.dionne@auristor.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>

fs/afs/rxrpc.c

@@ -61,6 +61,10 @@ int afs_open_socket(struct afs_net *net)
 	srx.transport.sin6.sin6_port	= htons(AFS_CM_PORT);
 
 	ret = kernel_bind(socket, (struct sockaddr *) &srx, sizeof(srx));
+	if (ret == -EADDRINUSE) {
+		srx.transport.sin6.sin6_port = 0;
+		ret = kernel_bind(socket, (struct sockaddr *) &srx, sizeof(srx));
+	}
 	if (ret < 0)
 		goto error_2;