Ignore SIGPIPE signals on write() failures.

We already check for write() failures and handle EPIPE.
Failure to handle SIGPIPE was resulting in rpc.lockd terminating.

PR:		bin/97768
Reported by:	Gea-Suan Lin <gslin at csie dot nctu dot edu dot tw>
MFC after:	1 day

usr.sbin/rpc.lockd/kern.c

@@ -151,6 +151,7 @@ client_request(void)
 
 	signal(SIGHUP, (sig_t)client_cleanup);
 	signal(SIGTERM, (sig_t)client_cleanup);
+	signal(SIGPIPE, SIG_IGN);
 
 	/* Setup. */
 	(void)time(&owner.tod);