{IPv6,xfrm} Add ESN support for AH egress part

This patch add esn support for AH output stage by attaching upper 32bits
sequence number right after packet payload as specified by RFC 4302.

Then the ICV value will guard upper 32bits sequence number as well when
packet going out.

Signed-off-by: Fan Du <fan.du@windriver.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>