Documentation: ip-sysctl.txt: clarify secure_redirects

Clarify how secure_redirects works. Mention that RFC1122 always applies.
Signed-off-by: NEric Garver <e@erig.me>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -1036,15 +1036,17 @@ proxy_arp_pvlan - BOOLEAN
 
 shared_media - BOOLEAN
 	Send(router) or accept(host) RFC1620 shared media redirects.
-	Overrides ip_secure_redirects.
+	Overrides secure_redirects.
 	shared_media for the interface will be enabled if at least one of
 	conf/{all,interface}/shared_media is set to TRUE,
 	it will be disabled otherwise
 	default TRUE
 
 secure_redirects - BOOLEAN
-	Accept ICMP redirect messages only for gateways,
-	listed in default gateway list.
+	Accept ICMP redirect messages only to gateways listed in the
+	interface's current gateway list. Even if disabled, RFC1122 redirect
+	rules still apply.
+	Overridden by shared_media.
 	secure_redirects for the interface will be enabled if at least one of
 	conf/{all,interface}/secure_redirects is set to TRUE,
 	it will be disabled otherwise