crypto: gcm - Add RFC4543 wrapper for GCM

This patch adds the RFC4543 (GMAC) wrapper for GCM similar to the
existing RFC4106 wrapper. The main differences between GCM and GMAC are
the contents of the AAD and that the plaintext is empty for the latter.

Signed-off-by: Tobias Brunner <tobias@strongswan.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/include/linux/pfkeyv2.h b/include/linux/pfkeyv2.h
index 228b0b6..0b80c80 100644
--- a/include/linux/pfkeyv2.h
+++ b/include/linux/pfkeyv2.h
@@ -315,6 +315,7 @@
 #define SADB_X_EALG_AES_GCM_ICV12	19
 #define SADB_X_EALG_AES_GCM_ICV16	20
 #define SADB_X_EALG_CAMELLIACBC		22
+#define SADB_X_EALG_NULL_AES_GMAC	23
 #define SADB_EALG_MAX                   253 /* last EALG */
 /* private allocations should use 249-255 (RFC2407) */
 #define SADB_X_EALG_SERPENTCBC  252     /* draft-ietf-ipsec-ciph-aes-cbc-00 */