The value of vRtrInetStaticRouteNextHopIf specifies the name of the
interface to be used for the next hop of this static route and it
depends on the value of vRtrInetStaticRouteStaticType.
At most only one of the values of the three objects:
vRtrInetStaticRouteNextHop, vRtrInetStaticRouteNextHopIf and
vRtrInetStaticRouteNHTunnelName can be a non null string.
If the value of vRtrInetStaticRouteStaticType is 'unknown' or
'blackHole' then the value of vRtrInetStaticRouteNextHopType should
be 'unknown' and the values of vRtrInetStaticRouteNextHop,
vRtrInetStaticRouteNextHopIf, vRtrInetStaticRouteNHTunnelName
should be null strings.