net: Add missing descriptions for fwmark_reflect for ipv4 and ipv6.

It was initially sent by Lorenzo Colitti, but was subsequently
lost in the final diff he submitted.
Signed-off-by: Loganaden Velvindron <logan@elandsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -56,6 +56,13 @@ ip_forward_use_pmtu - BOOLEAN
 	0 - disabled
 	1 - enabled
 
+fwmark_reflect - BOOLEAN
+	Controls the fwmark of kernel-generated IPv4 reply packets that are not
+	associated with a socket for example, TCP RSTs or ICMP echo replies).
+	If unset, these packets have a fwmark of zero. If set, they have the
+	fwmark of the packet they are replying to.
+	Default: 0
+
 route/max_size - INTEGER
 	Maximum number of routes allowed in the kernel.  Increase
 	this when using large numbers of interfaces and/or routes.
@@ -1201,6 +1208,13 @@ conf/all/forwarding - BOOLEAN
 proxy_ndp - BOOLEAN
 	Do proxy ndp.
 
+fwmark_reflect - BOOLEAN
+	Controls the fwmark of kernel-generated IPv6 reply packets that are not
+	associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
+	If unset, these packets have a fwmark of zero. If set, they have the
+	fwmark of the packet they are replying to.
+	Default: 0
+
 conf/interface/*:
 	Change special settings per interface.