examples/ipsec-secgw: support AES 256

Adding support for AES 256 algorithm in ipsec-secgw application

Signed-off-by: Anoob Joseph <anoob.joseph@caviumnetworks.com>
Acked-by: Radu Nicolau <radu.nicolau@intel.com>

doc/guides/sample_app_ug/ipsec_secgw.rst

@@ -395,6 +395,7 @@ where each options means:
 
    * *null*: NULL algorithm
    * *aes-128-cbc*: AES-CBC 128-bit algorithm
+   * *aes-256-cbc*: AES-CBC 256-bit algorithm
    * *aes-128-ctr*: AES-CTR 128-bit algorithm
 
  * Syntax: *cipher_algo <your algorithm>*

examples/ipsec-secgw/sa.c

@@ -68,6 +68,13 @@ const struct supported_cipher_algo cipher_algos[] = {
 		.block_size = 16,
 		.key_len = 16
 	},
+	{
+		.keyword = "aes-256-cbc",
+		.algo = RTE_CRYPTO_CIPHER_AES_CBC,
+		.iv_len = 16,
+		.block_size = 16,
+		.key_len = 32
+	},
 	{
 		.keyword = "aes-128-ctr",
 		.algo = RTE_CRYPTO_CIPHER_AES_CTR,