Adjust local_rpcb() definition to avoid clang 15 warning

With clang 15, the following -Werror warning is produced:

    sys/rpc/rpcb_clnt.c:439:11: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
    local_rpcb()
              ^
               void

This is because local_rpcb() is declared with a (void) argument list,
but defined with an empty argument list. Make the definition match the
declaration.

MFC after:	3 days

sys/rpc/rpcb_clnt.c

@@ -436,7 +436,7 @@ getclnthandle(host, nconf, targaddr)
  * rpcbind. Returns NULL on error and free's everything.
  */
 static CLIENT *
-local_rpcb()
+local_rpcb(void)
 {
 	CLIENT *client;
 	struct socket *so;