ip: factor out protocol delivery helper

So that we can re-use it at the UDP level in a later patch

rfc v3 -> v1
 - add the helper declaration into the ip header

Change-Id: I5dd1f510dc689a7370c09882985d0ee0dcb2ede4
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git


Git-commit: 68cb7d531e6a87250a51b8a4ee1c79b3445aeff3
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>