This is used to modify the IPv6 HOPLIMIT header field.  The HOPLIMIT field is 
similar to what is known as TTL value in IPv4.  Setting or incrementing the
HOPLIMIT field can potentially be very dangerous, so it should be avoided at
any cost.  
.TP
.B Don't ever set or increment the value on packets that leave your local network!
.B mangle
table.
.TP
.BI "--hl-set " "value"
Set the HOPLIMIT value to `value'.
.TP
.BI "--hl-dec " "value"
Decrement the HOPLIMIT value `value' times.
.TP
.BI "--hl-inc " "value"
Increment the HOPLIMIT value `value' times.