Documentation: networking: explain what happens if temp_prefered_lft is too small or too large

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20231024212312.299370-5-alexhenrie24@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/ip-sysctl.rst

@@ -2509,7 +2509,11 @@ temp_valid_lft - INTEGER
 	Default: 172800 (2 days)
 
 temp_prefered_lft - INTEGER
-	Preferred lifetime (in seconds) for temporary addresses.
+	Preferred lifetime (in seconds) for temporary addresses. If
+	temp_prefered_lft is less than the minimum required lifetime (typically
+	5 seconds), the preferred lifetime is the minimum required. If
+	temp_prefered_lft is greater than temp_valid_lft, the preferred lifetime
+	is temp_valid_lft.
 
 	Default: 86400 (1 day)