veth.4: Elaborate on use of ethtool(8) to find veth peer

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man4/veth.4

@@ -49,7 +49,6 @@ In the above,
 and
 .I p2-name
 are the names assigned to the two connected end points.
-interconnected with each other.
 .PP
 Packets transmitted on one device in the pair are immediately received on
 the other device.
@@ -64,9 +63,21 @@ pair in one network namespace and the other end in another network namespace,
 thus allowing communication between network namespaces.
 .PP
 .BR ethtool (8)
-can be used to test if a networking device is a
+can be used to find the peer of a
 .B veth
-device, and to find the peer network interface.
+network interface, using commands something like:
+.PP
+.in +4n
+.EX
+# \fBip link add ve_A type veth peer name ve_B\fP    # Create veth pair
+# \fBethtool -S ve_A\fP     # Discover interface index of peer
+NIC statistics:
+     peer_ifindex: 16
+# \fBip link | grep '^16:'\fP    # Look up interface
+16: ve_B@ve_A: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc ...
+.EE
+.in
+.PP
 .SH "SEE ALSO"
 .BR clone (2),
 .BR ip (8),