[nrf fromlist] net: fix configuration of NET_LINK_ADDR_MAX_LENGTH

Replace `CONFIG_NET_L2_IEEE802154` with `CONFIG_NET_L2_PHY_IEEE802154`
as `NET_LINK_ADDR_MAX_LENGTH` should be set to `8` for all IEEE 802.15.4
based L2, e.g. OpenThread.

Upstream PR #: 89477

Signed-off-by: Adrian Gielniewski <[email protected]>
(cherry picked from commit c3768dc6b8a6945b763b0c1abf01a5ecd48864ce)

Author: adigie

include/zephyr/net/net_linkaddr.h

@@ -30,15 +30,11 @@ extern "C" {
  */
 
 /** Maximum length of the link address */
-#ifdef CONFIG_NET_L2_IEEE802154
-#define NET_LINK_ADDR_MAX_LENGTH 8
-#else
-#ifdef CONFIG_NET_L2_PPP
+#if defined(CONFIG_NET_L2_PHY_IEEE802154) || defined(CONFIG_NET_L2_PPP)
 #define NET_LINK_ADDR_MAX_LENGTH 8
 #else
 #define NET_LINK_ADDR_MAX_LENGTH 6
 #endif
-#endif
 
 /**
  * Type of the link address. This indicates the network technology that this