aead: Support custom AEAD salt sizes

The salt, or often called implicit nonce, varies between AEAD algorithms and
their use in protocols. For IKE and ESP, GCM uses 4 bytes, while CCM uses
3 bytes. With TLS, however, AEAD mode uses 4 bytes for both GCM and CCM.

Our GCM backends currently support 4 bytes and CCM 3 bytes only. This is fine
until we go for CCM mode support in TLS, which requires 4 byte nonces.

src/libipsec/esp_context.c

@@ -216,7 +216,8 @@ static bool create_aead(private_esp_context_t *this, int alg,
 		case ENCR_AES_GCM_ICV12:
 		case ENCR_AES_GCM_ICV16:
 			/* the key includes a 4 byte salt */
-			this->aead = lib->crypto->create_aead(lib->crypto, alg, key.len-4);
+			this->aead = lib->crypto->create_aead(lib->crypto, alg,
+												  key.len - 4, 4);
 			break;
 		default:
 			break;