doc: add missing auth algo for IPsec example

[ upstream commit d05828a ]

Adding the missing SHA256-HMAC authentication algorithm
in ipsec-secgw guide.

Fixes: b535028 ("examples/ipsec-secgw: support SHA256 HMAC")

Signed-off-by: Gagandeep Singh <g.singh@nxp.com>
Acked-by: Akhil Goyal <gakhil@marvell.com>

doc/guides/sample_app_ug/ipsec_secgw.rst

@@ -106,7 +106,8 @@ Constraints
 
 *  No IPv6 options headers.
 *  No AH mode.
-*  Supported algorithms: AES-CBC, AES-CTR, AES-GCM, 3DES-CBC, HMAC-SHA1 and NULL.
+*  Supported algorithms: AES-CBC, AES-CTR, AES-GCM, 3DES-CBC, HMAC-SHA1,
+   HMAC-SHA256 and NULL.
 *  Each SA must be handle by a unique lcore (*1 RX queue per port*).
 
 Compiling the Application
@@ -564,6 +565,7 @@ where each options means:
 
     * *null*: NULL algorithm
     * *sha1-hmac*: HMAC SHA1 algorithm
+    * *sha256-hmac*: HMAC SHA256 algorithm
 
 ``<auth_key>``