ipsec: fix transport mode for IPv6 with extensions

ipsec: fix transport mode for IPv6 with extensions

Reconstructing IPv6 header after encryption or decryption requires
updating 'next header' value in the preceding protocol header, which
is determined by parsing IPv6 header and iteratively looking for
next IPv6 header extension.

It is required that 'l3_len' in the mbuf metadata contains a total
length of the IPv6 header with header extensions up to ESP header.

Fixes: 4d7ea3e1459b ("ipsec: implement SA data-path API")
Cc: stable@dpdk.org
Signed-off-by: Marcin Smoczynski <marcinx.smoczynski@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>
Tested-by: Konstantin Ananyev <konstantin.ananyev@intel.com>