Added support for configuring IGTK

This needs changes in kernel code, too, but the cipher suite for IGTK is
defined in IEEE 802.11w, so this code in hostapd side can be added now.

hostapd/driver_nl80211.c

@@ -208,8 +208,13 @@ static int i802_set_encryption(const char *iface, void *priv, const char *alg,
 			NLA_PUT_U32(msg, NL80211_ATTR_KEY_CIPHER, 0x000FAC02);
 		else if (strcmp(alg, "CCMP") == 0)
 			NLA_PUT_U32(msg, NL80211_ATTR_KEY_CIPHER, 0x000FAC04);
-		else
+		else if (strcmp(alg, "IGTK") == 0)
+			NLA_PUT_U32(msg, NL80211_ATTR_KEY_CIPHER, 0x000FAC06);
+		else {
+			wpa_printf(MSG_ERROR, "%s: Unsupported encryption "
+				   "algorithm '%s'", __func__, alg);
 			goto out;
+		}
 	}
 
 	if (addr)