main: introduce -D as quick acess to debugging

src/main.c

@@ -582,7 +582,7 @@ static int parse_argv(int argc, char *argv[]) {
         assert(argc >= 1);
         assert(argv);
 
-        while ((c = getopt_long(argc, argv, "h", options, NULL)) >= 0)
+        while ((c = getopt_long(argc, argv, "hD", options, NULL)) >= 0)
 
                 switch (c) {
 
@@ -715,6 +715,10 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_action = ACTION_HELP;
                         break;
 
+                case 'D':
+                        log_set_max_level(LOG_DEBUG);
+                        break;
+
                 case '?':
                         return -EINVAL;