staging: r8188eu: use ieee80211 structs for addresses

Map the incoming frame data to a struct ieee80211_hdr and extract
the addresses.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220403164526.357371-5-martin@kaiser.cx


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