Fix VLAN name persistence across rename and delete operations

Previously, renaming a VLAN or deleting and recreating it with a
different name did not update the displayed name. The vlan_names[]
array is an append-only buffer where vlan_name() returns the first
matching entry, so stale entries kept winning.

This commit adds vlan_name_remove(), which locates an entry by
VLAN ID and removes it via array compaction. The function is called
in two places:

  - parse_vlan() in cmd_parser.c, before appending a new name entry,
    to remove any pre-existing entry for the same VLAN ID
  - vlan_delete() in rtl837x_port.c, to clean up the name when a
    VLAN is removed

The implementation reuses the existing vlan_name() lookup, scans for
the trailing space of the matched entry, then shifts remaining bytes
left. Locals are declared as static __xdata to avoid the SDCC
overlay segment limit on banked functions.

Tested on KeepLiNK KP-9000-6XH-X:
  - vlan 99 AAA p1u; vlan 99 BBB -> name updated to BBB
  - vlan 99 d; vlan 99 CCC p1u   -> name correctly CCC, not stale AAA

Note: This fix addresses the runtime XMEM state. Persistence of
renamed VLAN names across reboot requires the user to download and
re-upload /config, as is the existing pattern for all configuration
changes in this firmware.

cmd_parser.c

@@ -347,6 +347,7 @@ void parse_vlan(void)
 		uint8_t w = 2;
 		if (cmd_words_len > w && isletter(cmd_buffer[cmd_words_b[w]])) {
 			register uint8_t i = 0;
+			vlan_name_remove(vlan_settings.vlan);
 			vlan_names[vlan_ptr++] = hex[(vlan_settings.vlan >> 8) & 0xf];
 			vlan_names[vlan_ptr++] = hex[(vlan_settings.vlan >> 4) & 0xf] ;
 			vlan_names[vlan_ptr++] = hex[vlan_settings.vlan & 0xf];

rtl837x_port.c

@@ -116,11 +116,45 @@ uint16_t port_pvid_get(uint8_t port) __banked
 void vlan_delete(uint16_t vlan) __banked
 {
 	print_string("\nvlan_delete called \n"); print_short(vlan);
+	vlan_name_remove(vlan);
 	REG_WRITE(RTL837x_TBL_DATA_IN_A, 0, 0, 0, 0);
 	REG_WRITE(RTL837X_TBL_CTRL, vlan >> 8, vlan, TBL_VLAN, TBL_WRITE | TBL_EXECUTE);
 }
 
 
+void vlan_name_remove(uint16_t vlan) __banked
+{
+	static __xdata uint16_t name_pos;
+	static __xdata uint16_t entry_start;
+	static __xdata uint16_t pos;
+	static __xdata uint16_t entry_len;
+	static __xdata uint16_t move_count;
+	static __xdata uint16_t j;
+
+	name_pos = vlan_name(vlan);
+	if (name_pos == 0xffff)
+		return;
+
+	entry_start = name_pos - 3;
+	pos = entry_start;
+
+	while (pos < vlan_ptr && vlan_names[pos] != ' ')
+		pos++;
+	if (pos >= vlan_ptr)
+		return;
+	pos++;
+
+	entry_len = pos - entry_start;
+	move_count = vlan_ptr - pos;
+
+	for (j = 0; j < move_count; j++)
+		vlan_names[entry_start + j] = vlan_names[pos + j];
+
+	vlan_ptr -= entry_len;
+	vlan_names[vlan_ptr] = 0;
+}
+
+
 /*
  * Reads VLAN information from VLAN table
  * Returns data in sfr_data

rtl837x_port.h

@@ -50,6 +50,7 @@ void port_l2_learned(void) __banked;
 void port_stats_print(void) __banked;
 int8_t vlan_get(register uint16_t vlan) __banked;
 __xdata uint16_t vlan_name(register uint16_t vlan) __banked;
+void vlan_name_remove(uint16_t vlan) __banked;
 void vlan_setup(void) __banked;
 void port_pvid_set(uint8_t port, __xdata uint16_t pvid) __banked;
 uint16_t port_pvid_get(uint8_t port) __banked;