Add `gre` and `mpls` containers under next-hops aft entry state. Add `ttl` and `tos` under gre, mpls and ip-in-ip aft entry state for telemetry.

[romeyod]

• (M) aft/openconfig-aft-common.yang
• (M) aft/openconfig-aft-ethernet.yang
• (M) aft/openconfig-aft-ipv4.yang
• (M) aft/openconfig-aft-ipv6.yang
• (M) aft/openconfig-aft-mpls.yang
• (M) aft/openconfig-aft-pf.yang
• (M) aft/openconfig-aft-state-synced.yang
• (M) aft/openconfig-aft.yang

Change Scope

• Add gre and mpls containers under next-hops aft entry state.
• Add ttl and tos under gre, mpls and ip-in-ip aft entry state for telemetry.
• This change is backwards compatible

Platform Implementations

• Arista documentation

Relevant pyang output:

module: openconfig-network-instance
  +--rw network-instances
     +--rw network-instance* [name]
        +--ro afts
        |  +--ro next-hops
        |     +--ro next-hop* [index]
        |        +--ro index            -> ../state/index
        |        +--ro state
        |        |  +--ro index?                       uint64
        |        |  +--ro programmed-index?            uint64
        |        |  +--ro ip-address?                  oc-inet:ip-address
        |        |  +--ro mac-address?                 oc-yang:mac-address
        |        |  +--ro pop-top-label?               boolean
        |        |  +--ro pushed-mpls-label-stack*     oc-mplst:mpls-label
        |        |  +--ro encapsulate-header?          oc-aftt:encapsulation-header-type
        |        |  +--ro decapsulate-header?          oc-aftt:encapsulation-header-type
        |        |  +--ro origin-protocol?             identityref
        |        |  +--ro lsp-name?                    string
        |        |  +--ro counters
        |        |  |  +--ro packets-forwarded?   oc-yang:counter64
        |        |  |  +--ro octets-forwarded?    oc-yang:counter64
        |        |  +--ro vni-label?                   oc-evpn-types:evi-id
        |        |  +--ro tunnel-src-ip-address?       oc-inet:ip-address
        |        |  +--ro oc-aftni:network-instance?   oc-ni:network-instance-ref
        |        +--ro ip-in-ip
        |        |  +--ro state
        |        |     +--ro src-ip?   oc-inet:ip-address
        |        |     +--ro dst-ip?   oc-inet:ip-address
        |        |     +--ro ttl?      uint32
        |        |     +--ro tos?      uint16
        |        +--ro gre
        |        |  +--ro state
        |        |     +--ro ttl?   uint32
        |        |     +--ro tos?   uint16
        |        +--ro mpls
        |        |  +--ro state
        |        |     +--ro ttl?   uint32
        |        |     +--ro tos?   uint16
        |        +--ro interface-ref
        |           +--ro state
        |              +--ro interface?      -> /oc-if:interfaces/interface/name
        |              +--ro subinterface?   -> /oc-if:interfaces/interface[oc-if:name=current()/../interface]/subinterfaces/subinterface/index