ipv6: factor out protocol delivery helper

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

rfc v3 -> v1:
 - add the helper declaration into the ipv6 header

Change-Id: I36df5e1c5cc4ccc2113b30c2f19a5f4cb10792e1
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: 80bde363f9a43d942e404821b966e362131cd0ca
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>