Fixes segfaults when running via monitoring worker

(off-by-one)

Grabed from https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=198318

plugins-root/check_dhcp.c

@@ -1194,7 +1194,7 @@ int call_getopt(int argc, char **argv){
 		        }
 	        }
 
-	return i;
+	return i+1;
         }