OP-1510 don't hard code tx_power to 100mW
OP-1522 Robustness of OPLink radio

Increase number of channels to 32 for all bit rates.
Synchronize clock on all channels.
Go into failsafe after 4 or 8 (one_way_link) missed packets.
Don't stay on channel 0 if we dropped a packet.
OP-1530 Use rfm22b_dev->num_channels

Use the number of allocated channel from the num_channels field
in the pios_rfm22b_dev struct rather than from the maximum number
of possible of channels given the configured speed.
Merge remote-tracking branch 'origin/havyan/oplink-0' into next