ANDROID: GKI: add vendor padding variable in struct skb_shared_info

Some vendors want to add things to 'struct skb_shared_info', so give
them an array to place their data.

Bug: 171013716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ifaa5942550794b747e9624124c785a0bc85dfe17