octphy: align frame number for new firmware versions
octphy: align frame number for new firmware versions

Firmware releases OCTSDR-2G-02.07.00-B1314-BETA and newer require
to align the GPRS frame number (fn-3) for ph_data indications.

To preserve compatibility the header version is checked during
compile time and the right method is compiled in.

Change-Id: Ib93d5fb3b34ff92f10021a0e9ce9c8aa3044b7ff

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts