[PATCH] bonding: inherit zero-copy flags of slaves

This change allows a bonding device to inherit the "zero-copy"
features of its slave devices.

It was inspired by a couple of previous postings on this topic:
http://marc.theaimsgroup.com/?l=bonding-devel&m=111924607327794&w=2
http://marc.theaimsgroup.com/?l=bonding-devel&m=111925242706297&w=2
and it's largely a combination of the patches that appear in those
emails.

Signed-off-by: Arthur Kepner <akepner@sgi.com>