staging: r8188eu: replace the GetFrameSubType call

The driver's local GetFrameSubType macro returns both frame type and
subtype.

Use the ieee80211 framework to extract the two fields. This shows more
clearly that both type and subtype are read.

Convert everything to host endianness before we use bit operations.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220417102221.466524-3-martin@kaiser.cx


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