wifi-scripts: introduce rxkh_file uci option

wifi-scripts: introduce rxkh_file uci option

With rxkh_file, hostapd will read a list of RxKHs from a text file.
This also makes it possible for hostapd to dynamically reload RxKHs.

RxKHs defined in rxkh_file should be formated as described in hostapd.conf,
with one entry per line.

R0KH/R1KH format:
r0kh=<MAC address> <NAS Identifier> <256-bit key as hex string>
r1kh=<MAC address> <R1KH-ID> <256-bit key as hex string>

Reworked behavior of the uci options r0kh and r1kh.

When rxkh_file is not configured:
  Instead of appending the RxKHs to the hostapd bss configuration.
  They will be added to a interface specific file with name
  /var/run/hostapd-phyX-apX.rxkh.
  This file will be used as the rxkh_file in the hostapd bss configuration.

When rxkh_file is configured:
  The specified file will be used in the hostapd bss configuration,
  and will be the only source for configured RxKHs.
  All RxKHs defined with the uci options r0kh or r1kh will be ignored.

Signed-off-by: Sybil127 <sybil127@outlook.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>