[AF_RXRPC]: Make call state names available if CONFIG_PROC_FS=n

Make the call state names array available even if CONFIG_PROC_FS is
disabled as it's used in other places (such as debugging statements)
too.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>