staging: r8188eu: use ieee80211 helpers to check the frame type

Use the ieee80211_is_... helper functions to check the frame type in
the validate_recv_frame function. Add a temporary variable for the
16-bit frame control field.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220227164147.1168847-3-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>