Fix "Get Configuration" on vlan.html

I noticed that entering some vlan config, clicking "Update/Create", then
clicking "Get Configuration" resulted in Tagged/Untagged/PVID displaying
completely wrong data. It looks like the parisng in fetchVLAN() in
vlan.js was just completely disconnected from the layout of the
registers read by vlan_get() in rtl837x_port.c. Who knows how that
happened.

1. Fix fetchVLAN() member/untag parsing: the old code read bits [9:0]
   as untagged and bits [10:19] as tagged, but the VLAN table register
   layout is members in [9:0] and untag in [19:10]. Now correctly
   derives tagged (member && !untag) and untagged (member && untag).

2. Add PVID to vlan.json response: PVID is stored per-port in separate
   PVID registers (RTL837x_PVID_BASE_REG), not in the VLAN table entry.
   The old code nonsensically tried to read it from bits [20:29] of the
   VLAN table. Add port_pvid_get() and build a pvid bitmask in
   send_vlan() so the JS can parse it correctly.

3. Remove auto-PVID logic from setC(): setC() is called by fetchVLAN()
   while it's loading existing config, and so this logic mangled the
   display of the existing config. Also, it doesn't make sense to
   auto-set the PVID for tagged members (PVID relates to untagged
   ingress.)

rtl837x_port.c

@@ -78,6 +78,17 @@ void port_pvid_set(uint8_t port, __xdata uint16_t pvid) __banked
 	}
 }
 
+uint16_t port_pvid_get(uint8_t port) __banked
+{
+	uint16_t reg = RTL837x_PVID_BASE_REG + ((port >> 1) << 2);
+	reg_read_m(reg);
+	if (port & 0x1) {
+		return (sfr_data[1] << 4) | (sfr_data[2] >> 4);
+	} else {
+		return ((sfr_data[2] & 0x0f) << 8) | sfr_data[3];
+	}
+}
+
 
 void vlan_delete(uint16_t vlan) __banked
 {