net: ieee802154: remove duplicate definition

`IEEE802154_MAX_ADDR_LENGTH` was defined in 2 headers, keep one only.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
diff --git a/include/net/ieee802154_mgmt.h b/include/net/ieee802154_mgmt.h
index db55adf..dfae51e 100644
--- a/include/net/ieee802154_mgmt.h
+++ b/include/net/ieee802154_mgmt.h
@@ -12,6 +12,7 @@
 #ifndef ZEPHYR_INCLUDE_NET_IEEE802154_MGMT_H_
 #define ZEPHYR_INCLUDE_NET_IEEE802154_MGMT_H_
 
+#include <net/ieee802154.h>
 #include <net/net_mgmt.h>
 
 #ifdef __cplusplus
@@ -26,9 +27,6 @@
  */
 
 
-#define IEEE802154_MAX_ADDR_LENGTH	8
-
-
 #define _NET_IEEE802154_LAYER	NET_MGMT_LAYER_L2
 #define _NET_IEEE802154_CODE	0x154
 #define _NET_IEEE802154_BASE	(NET_MGMT_IFACE_BIT |			\