Sets the Bluetooth transmit power level
Only available on the imp004m 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.