I spent my days to find a solution for that. I am currently on 5.0.1 Samsung note 4 and has ported nethunter with modded kernel. Only thing i cant figure out is to change my external wifi adapters' tx power (TL WN722N or Edimax Nano). Internal adapter (bcm4358) shows a 31 dbm txpower and channels 1-13 but whenever i plug a external wifi adapter, the external adapters txpower stuck at 20dbm (1-11 channels). I have tried iw solutions, regulatory.binadjustment and even txpower application on play store. I also tried one more solution from one forum to change the wifi country code etc. None of them worked for me so far. Why are developers silent about this issue? The only closest topic i found is only one at nethunter forums. Can anyone please help me?