Enable SR-MPLS transport for EVPN

[DanPartelly]

As the title says, we should add sr-mpls to the supported evpn.transport families, and start then to combine device configurations from the most used and to add support where possible.

@ipspace: Any comments? Any thoughts on how you would want this one done?

[ipspace]

Sure, let's do it ;) Enabling SR-MPLS support should be trivial, as the EVPN (configuration) part is unchanged. However, we don't support EVPN-with-MPLS on many devices, but maybe it's time that changes ;)

I'll add the necessary changes to the EVPN module, and hope EOS works out of the box. Then the fun starts ;))