Sets the Bluetooth transmit power level
Only available on the imp004m (impOS 38+) and imp006 (impOS 42+)
Transmission power in dBm
This method sets the transmit power level for advertisements and scan responses. The parameter power is an integer in the range -16 to +4, with values that are not a multiple of four being truncated (ie. -1 and -3 will be interpreted as -4). Passing in a value outside of this range will cause an exception to be thrown. The default (prior to calling this function after each bluetooth.open() and maximum transmit power is +4dBm.
The transmit power level can be altered whether or not advertising is enabled.