Usrp fix adc shift and pps sync
This MR fixes issues with the N310
- we were not using the right RX gain offset tables for N310. We now set the RX gain offsets for the N310 to zero, which means that the RX gain from the config file is the RX gain sent directly to the USRP.
- the right shift of the RX signal by 4 bits was not done for the N310.
- also made sure the pps sync is used to synchronize frames to pps boundary