comgt: ncm: support Mikrotik R11e-LTE6 modem

comgt: ncm: support Mikrotik R11e-LTE6 modem

The Mikrotik R11e-LTE6 modem is similar to ZTE MF286R modem, added
earlier: it has a Marvel chip, able to work in ACM+RNDIS mode, knows ZTE
specific commands, runs OpenWrt Barrier Breaker fork.
While the modem is able to offer IPv6 address, the RNDIS setup is unable
to complete if there is an IPv6 adress.

While it works in ACM+RNDIS mode, the user experience isn't as good as
with "proto 3g": the modem happily serves a local IP (192.168.1.xxx)
without internet access. Of course, if the modem has enough time
(for example at the second dialup), it will serve a public IP.

Modifing the DHCP Lease (to a short interval before connect and back to
default while finalizing) is a workaround to get a public IP at the
first try.

A safe workaround for this is to excercise an offline script of the
pingcheck program: simply restart (ifdown - ifup) the connection.

Another pitfall is that the modem writes a few messages at startup,
which confuses the manufacturer detection algorithm and got disabled.

    daemon.notice netifd: Interface 'mikrotik' is setting up now
    daemon.notice netifd: mikrotik (2366): Failed to parse message data
    daemon.notice netifd: mikrotik (2366): WARNING: Variable 'ok' does not exist or is not an array/object
    daemon.notice netifd: mikrotik (2366): Unsupported modem
    daemon.notice netifd: mikrotik (2426): Stopping network mikrotik
    daemon.notice netifd: mikrotik (2426): Failed to parse message data
    daemon.notice netifd: mikrotik (2426): WARNING: Variable '*simdetec:1,sim' does not exist or is not an array/object
    daemon.notice netifd: mikrotik (2426): Unsupported modem
    daemon.notice netifd: Interface 'mikrotik' is now down

A workaround for this is to use the "delay" option in the interface
configuration.

I want to thank Forum members dchard (in topic Adding support for
MikroTik hAP ac3 LTE6 kit (D53GR_5HacD2HnD)) [1]
and mrhaav (in topic OpenWrt X86_64 + Mikrotik R11e-LTE6) [2]
for sharing their experiments and works.
Another information page was found at eko.one.pl [3].

[1]: https://forum.openwrt.org/t/137555
[2]: https://forum.openwrt.org/t/151743
[3]: https://eko.one.pl/?p=modem-r11elte

Signed-off-by: Szabolcs Hubai <szab.hu@gmail.com>