Add serial numbers to JSON output

Serial numbers are now included in the JSON output for devices that have them.
This completes the JSON output enhancements to match the text output.

Example:
  "serial": "00015919101424154549"

Author: benroeder

uhubctl.c

@@ -1452,15 +1452,9 @@ char* create_port_status_json(int port, int port_status, const struct descriptor
     char *flags_json = create_status_flags_json(port_status);
     char *hr_json = create_human_readable_json(port_status);
 
-    // For USB3 hubs, get link state and port speed capability
+    // For USB3 hubs, get link state
     const char* link_state_str = NULL;
-    const char* port_speed_str = NULL;
     if (port_status & USB_SS_PORT_STAT_POWER) {
-        // Check port speed capability
-        if ((port_status & USB_SS_PORT_STAT_SPEED) == USB_PORT_STAT_SPEED_5GBPS) {
-            port_speed_str = "5gbps";
-        }
-        
         int link_state = port_status & USB_PORT_STAT_LINK_STATE;
         switch (link_state) {
             case USB_SS_PORT_LS_U0:          link_state_str = "U0"; break;
@@ -1526,7 +1520,7 @@ char* create_port_status_json(int port, int port_status, const struct descriptor
 
     // Return port with basic device info
     // Note: even when ignored, parameters still count towards total
-    return mkjson(MKJSON_OBJ, 16,
+    return mkjson(MKJSON_OBJ, 17,
         MKJSON_INT, "port", port,
         MKJSON_STRING, "status", status_hex,
         MKJSON_JSON_FREE, "flags", flags_json,
@@ -1541,6 +1535,7 @@ char* create_port_status_json(int port, int port_status, const struct descriptor
         MKJSON_STRING, "usb_version", usb_version,
         MKJSON_STRING, "device_version", device_version,
         MKJSON_INT, "nconfigs", desc.bNumConfigurations,
+        ds->serial[0] ? MKJSON_STRING : MKJSON_IGN_STRING, "serial", ds->serial,
         is_mass_storage ? MKJSON_BOOL : MKJSON_IGN_BOOL, "is_mass_storage", is_mass_storage,
         MKJSON_STRING, "description", ds->description[0] ? ds->description : NULL
     );