staging: r8188eu: use ieee80211_mgmt in issue_action_BA

Define a struct ieee80211_mgmt variable in issue_action_BA, this will make
it much simpler to populate the fields of the outoing frame.

Use the new mgmt variable to set the type and subtype of the frame.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220524090029.242584-4-martin@kaiser.cx


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