Initialize sockbits variable with FD_ZERO, to avoid passing a fd_set

with random garbage in lower bits corresponding to stdin, stdout and
stderr to select(2).

This fixes the problem with nfsd sometimes getting stuck in a tight
select(2) loop eating 100% CPU time.

Reviewed by:	iedowse
Approved by:	obrien

usr.sbin/nfsd/nfsd.c

@@ -355,6 +355,7 @@ main(argc, argv, envp)
 	(void)signal(SIGUSR1, cleanup);
 	FD_ZERO(&v4bits);
 	FD_ZERO(&v6bits);
+	FD_ZERO(&sockbits);
  
 	rpcbregcnt = 0;
 	/* Set up the socket for udp and rpcb register it. */