Unique number for this router within a given domain.
The router number (in combination with a VLAN ID) is
used as an identifier for an XRRP instance within a
domain. Along with 'hpicfXrrpDomain' it is used to
create the XRRP MAC address for the XRRP instance this
router owns. No two routers in the same domain can have
the same router number in the same level 2 switching
fabric.