staging: r8188eu: use ieee80211_mgmt for action category

Use the struct ieee80211_mgmt from ieee80211.h to read the action
category. There's no need to parse the incoming frame ourselves.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220502200652.143665-8-martin@kaiser.cx


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