ar71xx/generic: enable Zyxel NBG6616 in kernel config again

The NBG6616 shares a config symbol with the NBG6716. It was accidentally
removed from the config when the ar71xx-tiny target was split off.

Fixes: 0cd5e85 ("ar71xx: create new ar71xx/tiny subtarget for 4MB flash devices")
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
(cherry picked from commit a4f4ddb)

Author: neocturne

target/linux/ar71xx/generic/config-default

@@ -123,6 +123,7 @@ CONFIG_ATH79_MACH_MYNET_REXT=y
 CONFIG_ATH79_MACH_MZK_W04NU=y
 CONFIG_ATH79_MACH_MZK_W300NH=y
 CONFIG_ATH79_MACH_N5Q=y
+CONFIG_ATH79_MACH_NBG6716=y
 CONFIG_ATH79_MACH_OM2P=y
 CONFIG_ATH79_MACH_OM5P=y
 CONFIG_ATH79_MACH_OM5P_AC=y