ath79: ZTE MF286R: add comgt-ncm to DEVICE_PACKAGES

ath79: ZTE MF286R: add comgt-ncm to DEVICE_PACKAGES

When adding support to the router's built-in modem, this required
package was omitted, because it was already enabled in the image
configuration in use for testing, and this went unnoticed.
In result, the modem still isn't fully supported in official images.
As it is the primary WAN interface, add the missing package.

Fixes: e02fb42c53ba ("comgt: support ZTE MF286R modem")
Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
(cherry picked from commit 8a1003c5986514d7a78f78b3ee94003837d82582)