net: if: Documentation missing for IPv4 ACD timeout variable

Add documentation for ACD timeout variable as it was missing.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

include/zephyr/net/net_if.h

@@ -104,6 +104,8 @@ struct net_if_addr {
 		struct {
 			/** Address conflict detection (ACD) timer. */
 			sys_snode_t acd_node;
+
+			/** ACD timeout value. */
 			k_timepoint_t acd_timeout;
 
 			/** ACD probe/announcement counter. */