datapath: Orphan frags in skb_zerocopy and handle errors

This is the ported version of commit 36d5fe6a with the same name from net-next.
Apart from the small datapath.c changes it adjust the compat layer files as
well. This is the original commit message:

"skb_zerocopy can copy elements of the frags array between skbs, but it doesn't
orphan them. Also, it doesn't handle errors, so this patch takes care of that
as well, and modify the callers accordingly. skb_tx_error() is also added to
the callers so they will signal the failed delivery towards the creator of the
skb."

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>