CLEANUP: src/fd.c: mask setsockopt with DISGUISE

we do not care of what is returned, let static analyzers to
know that
diff --git a/src/fd.c b/src/fd.c
index d026b15..1934bd0 100644
--- a/src/fd.c
+++ b/src/fd.c
@@ -314,8 +314,8 @@
 
 	if (fdtab[fd].linger_risk) {
 		/* this is generally set when connecting to servers */
-		setsockopt(fd, SOL_SOCKET, SO_LINGER,
-			   (struct linger *) &nolinger, sizeof(struct linger));
+		DISGUISE(setsockopt(fd, SOL_SOCKET, SO_LINGER,
+			   (struct linger *) &nolinger, sizeof(struct linger)));
 	}
 	if (cur_poller.clo)
 		cur_poller.clo(fd);