ipsec: allow null cipher with dpdk esp

The NULL cipher is a (valid) non-AEAD choice for ESP encrypt path.
Allow it.

Type: fix
Signed-off-by: Christian E. Hopps <chopps@chopps.org>
Change-Id: I6d8b66223a0ffb0952c2dd6fa898a8a2289fef7a
diff --git a/src/plugins/dpdk/ipsec/esp_encrypt.c b/src/plugins/dpdk/ipsec/esp_encrypt.c
index 4d57909..1d29841 100644
--- a/src/plugins/dpdk/ipsec/esp_encrypt.c
+++ b/src/plugins/dpdk/ipsec/esp_encrypt.c
@@ -511,7 +511,8 @@
 	  u64 digest_paddr =
 	    mb0->buf_physaddr + digest - ((u8 *) mb0->buf_addr);
 
-	  if (!is_aead && cipher_alg->alg == RTE_CRYPTO_CIPHER_AES_CBC)
+	  if (!is_aead && (cipher_alg->alg == RTE_CRYPTO_CIPHER_AES_CBC ||
+			   cipher_alg->alg == RTE_CRYPTO_CIPHER_NULL))
 	    {
 	      cipher_off = sizeof (esp_header_t);
 	      cipher_len = iv_size + pad_payload_len;