nl80211: Fix NL80211_MESHCONF_AUTO_OPEN_PLINKS encoding

This nl80211 attribute uses NLA_U8 policy in cfg80211 and wpa_supplicant
needs to use same size when writing the attribute.

This fixes mesh mode regression triggered by kernel commit "net:
netlink: Update attr validation to require exact length for some types"
in v4.15-rc1 that resulted in the following debug log entry when trying
to join a mesh:
nl80211: mesh join failed: ret=-22 (Invalid argument)

Fixes: 6c1664f6051f ("nl80211: Add new commands to support mesh interfaces")
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/drivers/driver_nl80211.c

@@ -9026,8 +9026,8 @@ static int nl80211_put_mesh_config(struct nl_msg *msg,
 		return -1;
 
 	if (((params->flags & WPA_DRIVER_MESH_CONF_FLAG_AUTO_PLINKS) &&
-	     nla_put_u32(msg, NL80211_MESHCONF_AUTO_OPEN_PLINKS,
-			 params->auto_plinks)) ||
+	     nla_put_u8(msg, NL80211_MESHCONF_AUTO_OPEN_PLINKS,
+			params->auto_plinks)) ||
 	    ((params->flags & WPA_DRIVER_MESH_CONF_FLAG_MAX_PEER_LINKS) &&
 	     nla_put_u16(msg, NL80211_MESHCONF_MAX_PEER_LINKS,
 			 params->max_peer_links)) ||