docs: admin-guide: fix printk_ratelimit explanation

The printk_ratelimit value accepts seconds, not jiffies (though it is
converted into jiffies internally). Update documentation to reflect
this.

Also, remove the statement about allowing 1 message in 5 seconds since
bursts up to 10 messages are allowed by default.

Finally, while we are here, mention default value for
printk_ratelimit_burst too.
Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/sysctl/kernel.rst

@@ -831,8 +831,8 @@ printk_ratelimit:
 =================
 
 Some warning messages are rate limited. printk_ratelimit specifies
-the minimum length of time between these messages (in jiffies), by
-default we allow one every 5 seconds.
+the minimum length of time between these messages (in seconds).
+The default value is 5 seconds.
 
 A value of 0 will disable rate limiting.
 
@@ -845,6 +845,8 @@ seconds, we do allow a burst of messages to pass through.
 printk_ratelimit_burst specifies the number of messages we can
 send before ratelimiting kicks in.
 
+The default value is 10 messages.
+
 
 printk_devkmsg:
 ===============