wimax/i2400m: firmware_check() encodes the firmware version in i2400m->fw_version

Upcoming modifications will need to test for the running firmware
version before activating a feature or not. This is helpful to
implement backward compatibility with older firmware versions.

Modify i2400m_firmware_check() to encode in i2400m->fw_version the
major and minor version numbers of the firmware interface.

As well, move the call to be done as the very first operation once we
have communication with the device during probe() [in
__i2400m_dev_start()]. This is needed so any operation that is
executed afterwards can determine which fw version it is talking to.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>