staging: rtl8723bs: add get_channel cfg80211 implementation

add get_channel cfg80211 implementation to let userspace
programs rely on nl80211 protocol to display channel
information.

Old iw dev output:

phy#0
	Interface wlan0
		ifindex 2
		wdev 0x1
		addr 34:c3:d2:73:eb:c7
		ssid Fabio
		type managed
		txpower 12.00 dBm

Fixed output:

phy#0
	Interface wlan0
		ifindex 2
		wdev 0x1
		addr 34:c3:d2:73:eb:c7
		ssid Fabio
		type managed
	new-->	channel 11 (2462 MHz), width: 20 MHz, center1: 2462 Mhz
		txpower 12.00 dBm

Signed-off-by: Fabio Aiuto <fabioaiuto83@gmail.com>
Link: https://lore.kernel.org/r/2f00479d8369b82b590291bb0edf27bc3041b0f0.1626533647.git.fabioaiuto83@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>