net: dhcpv6: Add configurable DUID buffer length

According to the `RFC8415` the length of the DUID is at least 1 octet
up to 128 octets. Now a user can choose buffer length without the need
for source code modification.

Signed-off-by: Marcin Gasiorek <[email protected]>

Author: MarGasiorek

include/zephyr/net/dhcpv6.h

@@ -38,11 +38,14 @@ enum net_dhcpv6_state {
 } __packed;
 
 #define DHCPV6_TID_SIZE 3
-#define DHCPV6_DUID_MAX_SIZE 20
+
+#ifndef CONFIG_NET_DHCPV6_DUID_MAX_LEN
+#define CONFIG_NET_DHCPV6_DUID_MAX_LEN 22
+#endif
 
 struct net_dhcpv6_duid_raw {
 	uint16_t type;
-	uint8_t buf[DHCPV6_DUID_MAX_SIZE];
+	uint8_t buf[CONFIG_NET_DHCPV6_DUID_MAX_LEN];
 } __packed;
 
 struct net_dhcpv6_duid_storage {

subsys/net/lib/dhcpv6/Kconfig

@@ -15,6 +15,13 @@ config NET_DHCPV6
 	select NET_MGMT_EVENT
 	depends on NET_IPV6 && NET_UDP
 
+config NET_DHCPV6_DUID_MAX_LEN
+	int "The maximum DUID length (not including a type code)"
+	range 1 128
+	default 22
+	help
+	  This will set the available number of bytes for the DUID.
+
 if NET_DHCPV6
 module = NET_DHCPV6
 module-dep = NET_LOG