rum: switch to ieee80211_add_channel_list_*()

• Use device's channel list instead of default one

(from ieee80211_init_channels()).

• Add ic_getradiocaps() method.

Added channels:
2GHz band: 12, 13 and 14.
5Ghz band: 34, 38, 42, 46 and 165.

Tested with WUSB54GC, STA / MONITOR modes.

Differential Revision: https://reviews.freebsd.org/D6125