nrf802154: Change timer frequency to match symbols rate
nrf802154: Change timer frequency to match symbols rate

ieee802.15.4 specifies 40 symbols as LIFS value and 12 symbols as SIFS
value. Furthermore, the 2.4Ghz DSSS mode has a symbol rate of
62.5Ksymbols/s. To have the LIFS and SIFS in the code match the timings
from the specification, the TIMER_FREQ must match the symbol rate of
62.5Ksymbol/s such that one tick of the timer equals one symbol in time.

toonst/RIOT,mfrey/RIOT,jasonatran/RIOT,basilfx/RIOT,smlng/RIOT,aeneby/RIOT,ant9000/RIOT,miri64/RIOT,kaspar030/RIOT,josephnoir/RIOT,mfrey/RIOT,jasonatran/RIOT,kYc0o/RIOT,josephnoir/RIOT,cladmi/RIOT,cladmi/RIOT,OTAkeys/RIOT,authmillenon/RIOT,rfuentess/RIOT,mtausig/RIOT,lazytech-org/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,toonst/RIOT,cladmi/RIOT,OlegHahm/RIOT,yogo1212/RIOT,miri64/RIOT,OTAkeys/RIOT,lazytech-org/RIOT,smlng/RIOT,josephnoir/RIOT,x3ro/RIOT,mtausig/RIOT,x3ro/RIOT,yogo1212/RIOT,toonst/RIOT,authmillenon/RIOT,smlng/RIOT,lazytech-org/RIOT,toonst/RIOT,authmillenon/RIOT,kaspar030/RIOT,kaspar030/RIOT,rfuentess/RIOT,RIOT-OS/RIOT,cladmi/RIOT,kaspar030/RIOT,ant9000/RIOT,lazytech-org/RIOT,mfrey/RIOT,ant9000/RIOT,miri64/RIOT,RIOT-OS/RIOT,aeneby/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,mtausig/RIOT,x3ro/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,miri64/RIOT,lazytech-org/RIOT,authmillenon/RIOT,kYc0o/RIOT,rfuentess/RIOT,jasonatran/RIOT,basilfx/RIOT,mfrey/RIOT,OlegHahm/RIOT,yogo1212/RIOT,kYc0o/RIOT,toonst/RIOT,smlng/RIOT,x3ro/RIOT,RIOT-OS/RIOT,aeneby/RIOT,kYc0o/RIOT,basilfx/RIOT,yogo1212/RIOT,jasonatran/RIOT,rfuentess/RIOT,mfrey/RIOT,josephnoir/RIOT,yogo1212/RIOT,aeneby/RIOT,basilfx/RIOT,kYc0o/RIOT,ant9000/RIOT,OTAkeys/RIOT,miri64/RIOT,kaspar030/RIOT,aeneby/RIOT,basilfx/RIOT,authmillenon/RIOT,smlng/RIOT,jasonatran/RIOT,x3ro/RIOT,ant9000/RIOT,cladmi/RIOT,mtausig/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,rfuentess/RIOT,josephnoir/RIOT,mtausig/RIOT