check_tcp: add --sni as alias for -N

for the sake of readability and compatibility with monitoring-plugins/monitoring-plugins#1614 .

plugins/check_tcp.c

@@ -429,6 +429,7 @@ process_arguments (int argc, char **argv)
 		{"help", no_argument, 0, 'h'},
 		{"ssl", no_argument, 0, 'S'},
 		{"certificate", required_argument, 0, 'D'},
+		{"sni", required_argument, 0, 'N'},
 		{0, 0, 0, 0}
 	};