multicast: T6746: flatten CLI by merging "multicast route" to "mroute" CLI tagNode
This will save an entire level for the configuration and there is no need for a
parent "multicast" node, as it will only have "route" as tagNode below.
Move set protocols static multicast route <x.x.x.x/y> to:
- set protocols static mroute <x.x.x.x/y>