brcmfmac: remove mode field from brcmf_cfg80211_vif structure

The nl80211 iftype was converted to a mode value and stored in
brcmf_cfg80211_vif structure. The value was used only within
brcmfmac driver to decide execution of conditional code. Better
use wireless_dev::iftype for that as the wdev is contained in
the brcmf_cfg80211_vif structure.

Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>