net/dhcpv6 : Expose to Kconfig

Expose configurations to Kconfig. Add conditional CFLAGS to avoid
conflicts with Kconfig.

examples/gnrc_border_router/Makefile.native.conf

@@ -4,9 +4,11 @@ ZEP_PORT_BASE ?= 17754
 ZEP_PORT_MAX := $(shell expr $(ZEP_PORT_BASE) + $(ZEP_DEVICES) - 1)
 
 CFLAGS += -DSOCKET_ZEP_MAX=$(ZEP_DEVICES)
-CFLAGS += -DCONFIG_DHCPV6_CLIENT_PFX_LEASE_MAX=$(ZEP_DEVICES)
 CFLAGS += -DASYNC_READ_NUMOF=$(shell expr $(ZEP_DEVICES) + 1)
 
+# Set CFLAGS if not being set via Kconfig
+CFLAGS += $(if $(CONFIG_KCONFIG_MODULE_DHCPV6),,-DCONFIG_DHCPV6_CLIENT_PFX_LEASE_MAX=$(ZEP_DEVICES))
+
 # -z [::1]:$PORT for each ZEP device
 TERMFLAGS += $(patsubst %,-z [::1]:%, $(shell seq $(ZEP_PORT_BASE) $(ZEP_PORT_MAX)))
 

sys/net/application_layer/Kconfig

@@ -13,3 +13,5 @@ rsource "gcoap/Kconfig"
 rsource "nanocoap/Kconfig"
 
 endmenu # CoAP
+
+rsource "dhcpv6/Kconfig"

sys/net/application_layer/dhcpv6/Kconfig

@@ -0,0 +1,19 @@
+# Copyright (c) 2020 Freie Universitaet Berlin
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+#
+menuconfig KCONFIG_MODULE_DHCPV6
+    bool "Configure DHCPv6"
+    depends on MODULE_DHCPV6
+    help
+        Configure DHCPv6 client using Kconfig.
+
+if KCONFIG_MODULE_DHCPV6
+
+config DHCPV6_CLIENT_PFX_LEASE_MAX
+    int "Maximum number of prefix leases to be stored"
+    default 1
+
+endif # KCONFIG_MODULE_DHCPv6