hostapd: Global control interface notifications

This commit implements hostapd global control interface notifications
infrastructure. hostapd global control interface clients issue
ATTACH/DETACH commands to register and deregister with hostapd
correspondingly - the same way as for any other hostapd/wpa_supplicant
control interface.

Change-Id: I5074ca790585b72e1345ed758ab2554c22169bae
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Git-commit: ee1e3f57b58498882adbfa75633b0931000f5264
Git-repo: git://w1.fi/srv/git/hostap.git
CRs-Fixed: 891455
diff --git a/hostapd/main.c b/hostapd/main.c
index e36c948..62d0775 100644
--- a/hostapd/main.c
+++ b/hostapd/main.c
@@ -561,6 +561,7 @@
 	interfaces.global_iface_path = NULL;
 	interfaces.global_iface_name = NULL;
 	interfaces.global_ctrl_sock = -1;
+	interfaces.global_ctrl_dst = NULL;
 
 	for (;;) {
 		c = getopt(argc, argv, "b:Bde:f:hKP:Ttu:vg:G:");