staging: rtl8188eu: remove enum WIFI_FRAME_SUBTYPE

staging: rtl8188eu: remove enum WIFI_FRAME_SUBTYPE

The values defined in enum WIFI_FRAME_SUBTYPE are the same the #define
IEEE80211_STYPE_xxx from <linux/ieee80211.h>.

Special care must be taken for control and data frame, because  the coding
of the frame type is not included in the IEEE80211_STYPE_xxx values and
must be added explicitly.

There is no problem for management frame because the type si coded as (0)
(in rtl8188eu) and (0x0000) (in <linux/ieee80211.h>).

Values used for control frame (WIFI_PSPOLL) must be OR'eded with
IEEE80211_FTYPE_CTL.

Values used for data frame (WIFI_DATA_NULL and WIFI_QOS_DATA_NULL) must be
OR'ed with IEEE80211_FTYPE_DATA.

Use theses values to avoid code duplication.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/7c1007d5706a42e0ba1fe805089fab523f9db7ea.1619953884.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>