Document use of obsolete version of VRRP on Dell OS10 (#1492)

Author: jbemmel

docs/caveats.md

@@ -231,6 +231,9 @@ devices.cumulus.libvirt.memory: 2048
 * At the same time, the *anycast* gateway is not supported on plain *ethernet* interfaces, so you need to use *VRRP* there.
 * Dell OS10 only allows configuring of the EVPN RD in the form `X.X.X.X:N.` By default, *netlab* uses `N:M` for L3VNI, so on this platform the L3VNI RD is derived from the Router-ID and the VRF ID as `router-id:vrf-id` (and the one generated by *netlab* is not used).
 
+### VRRP Caveats
+VRRP on Dell defaults to version 2 - version 3 is only enabled when IPv6 is used on the node (i.e. ```af.ipv6=True```)
+
 (caveats-dnsmasq)=
 ## dnsmasq DHCP server