Felix programs IPIP tunnels

[mazdakn]

Description

Currently, it's BIRD that programs routes for IPIP encapsulation, which is unlike VXLAN|Wireguard where Felix programs the routes. This PR enables Felix to programs the IPIP routes as well, and not rely on BIRD anymore. The benefits are:

• Not needing an extra component (i.e. BIRD) for IPIP encapsulation. Enabling Felix to program IPIP routes and not running BIRD saves some memory/CPU.
• Allowing to get rid of Calico fork of BIRD (v1.6) which is way old. Instead we can use upstream BIRD.
• In future, we can also make Felix program no encap routes as well. and get rid of internal BGP mesh.

This PR includes:

• Adding support to Felix to program IPIP routes.
• Updating BIRD templates to not export IPIP routes, i.e routes with tunl0 interface.
• Updating BIRD templates to not program IPIP routes to kernel
• Introducing a new value of ipip for calico_backend variable to enable IPIP encapsulation without running BIRD. bird value still enables IPIP encapsulation and also start BIRD service.

Related issues/PRs

Todos

• [x] Tests
• [ ] Documentation
• [ ] Release note

Release Note

TBD

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