ZTE MF286R modem support

[Lech Perczak]

Hello,

Recently my PR #9670 [1] which includes fixes needed to support built-in 
modem of ZTE MF286R router was merged to master. The (incomplete) 
support for MF286R landed together with MF286A before branching off 
22.03 release.
I'd be grateful if fixes from [1] could be cherry-picked to 22.03, for 
MF286R to have full support in that release.

Required commits are c99013e, b2940bb, ed79578 and e02fb42, a67629b is 
optional, but would be beneficial if another variant of the modem is 
found, with different interface configuration - that may require to 
override the autodetection results. Also, skipping that patch can yield 
merge conflicts.

[1] https://github.com/openwrt/openwrt/pull/9670

-- 
Pozdrawiam/Kind regards,
Lech Perczak