staging: r8188eu: read back action code from ieee80211_mgmt

Read the back action code from struct ieee80211_mgmt.

struct ieee80211_mgmt contains an "action" union. Each of its members
starts with an 8-bit action code. Treat the union as addba_req when we
read the action code although we do not yet know if it is an addba_req.
This approach is similar to ieee80211_iface_process_skb.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220508161451.115847-6-martin@kaiser.cx


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