MACsec: Support GCM-AES-256 cipher suite

Allow macsec_csindex to be configured and select the cipher suite when
the participant acts as a key server.

Signed-off-by: leiwei <quic_leiwei@quicinc.com>

src/ap/ap_config.h

@@ -848,6 +848,13 @@ struct hostapd_bss_config {
 	 */
 	int mka_priority;
 
+	/**
+	 * macsec_csindex - Cipher suite index for MACsec
+	 *
+	 * Range: 0-1 (default: 0)
+	 */
+	int macsec_csindex;
+
 	/**
 	 * mka_ckn - MKA pre-shared CKN
 	 */