staging: rtl8192u: Merge almost duplicate code

staging: rtl8192u: Merge almost duplicate code

This causes a change in behaviour:
- stats also get updated when reordering, this seems like it should be
  the case but those lines were commented out.
- sub_skb NULL check now happens early in both cases, previously it
  happened only after dereferencing it 12 times, so it may not actually
  be needed.

Signed-off-by: Pascal Terjan <pterjan@google.com>
Link: https://lore.kernel.org/r/20200519150042.199690-1-pterjan@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>