CLEANUP: sockpair: silence a coverity check about fcntl()

This is about coverity complaining that we didn't check the fcntl call
which can't fail, let's consume it. This is issue #1158.
diff --git a/src/proto_sockpair.c b/src/proto_sockpair.c
index ca4fc6d..306213e 100644
--- a/src/proto_sockpair.c
+++ b/src/proto_sockpair.c
@@ -479,7 +479,7 @@
 	int cfd;
 
 	if ((cfd = recv_fd_uxst(l->rx.fd)) != -1)
-		fcntl(cfd, F_SETFL, O_NONBLOCK);
+		DISGUISE(fcntl(cfd, F_SETFL, O_NONBLOCK));
 
 	if (likely(cfd != -1)) {
 		/* Perfect, the connection was accepted */