modem: quectel-bg9x: implement 'is_supported' socket offload cb
modem: quectel-bg9x: implement 'is_supported' socket offload cb

Check if requested socket family, type and protocol are all supported by
the driver, instead of blindly acknowledging every possible variant.

There is explicit support for TCP on top of IPv4 and IPv6.

Signed-off-by: Marcin Niestroj <63506c06cfbc47ace147db1702f6e751f5ac2132@emb.dev>

galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr