staging: r8188eu: use mgmt to set the sequence number

Use the mgmt structure in issue_action_BA to set the sequence number of
the outgoing frame.

pwlanhdr is now unused, it can be removed.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220524090029.242584-6-martin@kaiser.cx


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