ipsec: fixed chaining ops after add footer and icv

ipsec: fixed chaining ops after add footer and icv

In case there is no free space in first buffer for ICV and footer,
additional buffer will be added, but esp_encrypt will stay in single
buffer mode.
The issue happens for the following payload sizes:
 - TCP packets with payload 1992
 - ICMP packets with payload 2004

This fix moves the single/chained buffer ops selection to after
esp_add_footer_and_icv call.

Type: fix

Signed-off-by: Fan Zhang <roy.fan.zhang@intel.com>
Signed-off-by: PiotrX Kleski <piotrx.kleski@intel.com>
Change-Id: Ic5ceba418f738933f96edb3e489ca2d149033b79