SUNRPC: Fix sparse warnings

 - net/sunrpc/xprtsock.c:1635:5: warning: symbol 'init_socket_xprt' was not
   declared. Should it be static?
 - net/sunrpc/xprtsock.c:1649:6: warning: symbol 'cleanup_socket_xprt' was
   not declared. Should it be static?

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>