Restructure log initilization function to allow multiple backends without arguments.

This patch ensures that we more easily can extend our log backends that
does not take any additional argument other than a single keyword. This
patch is mostly reindentation of some code which is why it is split out
into its own patch.

See: https://bugs.torproject.org/24362

src/or/config.c

@@ -5732,16 +5732,17 @@ options_init_logs(const or_options_t *old_options, or_options_t *options,
       }
       goto cleanup;
     }
-    if (smartlist_len(elts) == 1 &&
-        !strcasecmp(smartlist_get(elts,0), "syslog")) {
+    if (smartlist_len(elts) == 1) {
+      if (!strcasecmp(smartlist_get(elts,0), "syslog")) {
 #ifdef HAVE_SYSLOG_H
-      if (!validate_only) {
-        add_syslog_log(severity, options->SyslogIdentityTag);
-      }
+        if (!validate_only) {
+          add_syslog_log(severity, options->SyslogIdentityTag);
+        }
 #else
-      log_warn(LD_CONFIG, "Syslog is not supported on this system. Sorry.");
+        log_warn(LD_CONFIG, "Syslog is not supported on this system. Sorry.");
 #endif /* defined(HAVE_SYSLOG_H) */
-      goto cleanup;
+        goto cleanup;
+      }
     }
 
     if (smartlist_len(elts) == 2 &&