OpenWrt support for Zyxel LTE5398-M904

[AndrewZ]

@strips

+CEREG: 0,5

5 is "Registered, roaming"

For the rest please see my post:

APN issues on ZyXEL LTE5398-M904

Disable MBN as shown here: Registration denied on Lebara Sim - #7 by AndrewZ Check/set the APN on the modem using a terminal as shown in the wiki: https://openwrt.org/docs/guide-user/network/wan/wwan/ltedongle#lte_or_5g_modem_preparation