Documentation: networking: explain what happens if temp_valid_lft is too small

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20231024212312.299370-4-alexhenrie24@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/ip-sysctl.rst

@@ -2502,7 +2502,9 @@ use_tempaddr - INTEGER
 		* -1 (for point-to-point devices and loopback devices)
 
 temp_valid_lft - INTEGER
-	valid lifetime (in seconds) for temporary addresses.
+	valid lifetime (in seconds) for temporary addresses. If less than the
+	minimum required lifetime (typically 5 seconds), temporary addresses
+	will not be created.
 
 	Default: 172800 (2 days)