ath79: add Ubiquiti Rocket M XW as alternate name to Bullet M XW

Ubiquiti Rocket M XW is a single-band, 2x2:2 external Wi-Fi AP, with optional
GPS receiver, with two external RP-SMA antenna connections, based on
AR9342 SoC. Two band variants exists, for 2.4GHz and 5GHz band, usable
with the same image.

Specs:
- CPU: Atheros AR9342 MIPS SoC at 535MHz
- RAM: 64MB DDR400
- ROM: 8MB SPI-NOR in SO16W package, MX25L6408E
- Wi-Fi Atheros AR9342 built-in 2x2:2 radio
- Ethernet: Atheros AR8035 PHY, limited to 100Mbps speeds due to
  magnetics
- Power: 24V passive PoE input.

Installation: please refer to Ubiquiti Bullet M2HP for documentation.

The device runs with exactly same image as the Bullet, and after fixes
in preceding commit, is fully functional again. Add the alternative name
to the build system.

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
(cherry picked from commit 54387fd)

target/linux/ath79/image/generic-ubnt.mk

@@ -28,6 +28,9 @@ TARGET_DEVICES += ubnt_bullet-ac
 define Device/ubnt_bullet-m-xw
   $(Device/ubnt-xw)
   DEVICE_MODEL := Bullet M
+  DEVICE_ALT0_VENDOR := Ubiquiti
+  DEVICE_ALT0_MODEL := Rocket M
+  DEVICE_ALT0_VARIANT := XW
   DEVICE_PACKAGES += rssileds
   SUPPORTED_DEVICES += bullet-m-xw
 endef