docs: Fix `first-interface-index` documentation
docs: Fix `first-interface-index` documentation

This fixes the `first-interface-index` section in the ENI docs where we
introduced a new default value and wanted to document that new default,
but by doing that accidentally changed a value in the examples.

This commit actually fixes the default value and reverts the example to
its proper meaning.

Ref: https://github.com/cilium/cilium/pull/14801
Fixes: 231a217ea99d ("docs: first-interface-index new ENI default")

Signed-off-by: Sebastian Wicki <db043b2055cb3a47b2eb0b5aebf4e114a8c24a5a@isovalent.com>

michi-covalent/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium