tests: Fix `bgp_srv6l3vpn_to_bgp_vrf2` topotest

tests: Fix `bgp_srv6l3vpn_to_bgp_vrf2` topotest

The `bgp_srv6l3vpn_to_bgp_vrf2` topotest tests the SRv6 IPv4 L3VPN
functionality. It applies the appropriate configuration in `bgpd` and
`zebra`, and then checks that the RIB is updated correctly.

The topotest expects to find the AS-Path in the RIB, which is only
present if the `bgp send-extra-data zebra` option is enabled in the
`bgpd` configuration.

Currently, the `bgp send-extra-data zebra` option is not set in the
`bgpd` configuration, which always causes the topotest to fail.

This commit fixes the `bgp_srv6l3vpn_to_bgp_vrf2` topotest by enabling
the `bgp send-extra-data zebra` option for both routers `r1` and `r2`.

Signed-off-by: Carmine Scarpitta <carmine.scarpitta@uniroma2.it>