phy: convert tx power value
phy: convert tx power value

This patch convert the tx power value from long to float to
support the IEEE-802.15.4 radio power setting values.

Signed-off-by: Varka Bhadram <2af78e27b8c15f3929acd171eee40b9b9bcbd73c@cdac.in>
Signed-off-by: Alexander Aring <d03dbcdedb9639e397df9b8578e8fc8274f4e6c4@gmail.com>

cfriedt/wpan-tools,cfriedt/wpan-tools