Goal: 

• Add "Adopting BGP environments to the  RHOSO data plane" (or something similar) to the Adoption limitations module under "Unsupported features": https://docs.redhat.com/en/documentation/red_hat_openstack_services_on_openshift/18.0/html-single/adopting_a_red_hat_openstack_platform_17.1_deployment/index#adoption-limitations_planning
• Add ifevals to the notes regarding BGP data plane adoption so that they appear upstream only. Add a hidden comment that we'll remove the ifevals when the BGP data plane adoption is supported.

Acceptance Criteria:

• The limitation and ifevals are added to the adoption guide.
• SME review/peer review.
• The PR is merged.