man: tc-csum.8: Add an example

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

man/man8/tc-csum.8

@@ -49,6 +49,21 @@ UDPLite header
 .TP
 .B SWEETS
 These are merely syntactic sugar and ignored internally.
+.SH EXAMPLES
+The following performs stateless NAT for incoming packets from 192.168.1.100 to
+new destination 18.52.86.120 (0x12345678 in hex). Assuming these are UDP
+packets, both IP and UDP checksums have to be recalculated:
+
+.RS
+.EX
+# tc qdisc add dev eth0 ingress handle ffff:
+# tc filter add eth0 prio 1 protocol ip parent ffff: \\
+	u32 match ip src 192.168.1.100/32 flowid :1 \\
+	action pedit munge ip dst set 0x12345678 pipe \\
+	csum ip and udp
+.EE
+.RE
+
 .SH SEE ALSO
 .BR tc (8),
 .BR tc-pedit (8)