staging: rtl8712: switch to common ieee80211 headers

staging: rtl8712: switch to common ieee80211 headers

This patch switches to <linux/ieee80211.h> and <net/cfg80211.h> and
deletes a lot of duplicate definitions plus many unused ones.

Non obvious changes:
- struct ieee80211_ht_cap is different enough that I preferred to keep
  (and rename) it for now.
- mcs_rate in translate_scan was not read after being set, so I deleted
  that part rather than using the renamed struct
- WLAN_CAPABILITY_BSS is replaced with WLAN_CAPABILITY_ESS which is the
  corresponding one with same value

Signed-off-by: Pascal Terjan <pterjan@google.com>
Link: https://lore.kernel.org/r/20200609194848.166130-1-pterjan@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>