net: Convert CONFIG_IP_DEFRAG to Kconfig

Convert CONFIG_IP_DEFRAG to Kconfig, update defconfigs, headers
and whitelist. This patch is a follow-up on a patch by Christian
Gmeiner with the added config/header/whitelist updates.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Reported-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/net/Kconfig b/net/Kconfig
index f2363e5..1a6fda9 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -22,4 +22,11 @@
 	  Support the 'nc' input/output device for networked console.
 	  See README.NetConsole for details.
 
+config IP_DEFRAG
+	bool "Support IP datagram reassembly"
+	default n
+	help
+	  Selecting this will enable IP datagram reassembly according
+	  to the algorithm in RFC815.
+
 endif   # if NET