hostapd: Add supported channel bandwidth checking infrastructure

hostapd: Add supported channel bandwidth checking infrastructure

This adds checks to common code to verify supported bandwidth options
for each channel using nl80211-provided info. No support of additional
modes is added, just additional checks. Such checks are needed because
driver/hardware can declare more strict limitations than declared in the
IEEE 802.11 standard. Without this patch hostapd might select
unsupported channel and that will fail because Linux kernel does check
channel bandwidth limitations.

Signed-off-by: Dmitry Lebed <dlebed@quantenna.com>