doc: BGP dynamic routing guide: replaced deprecated bgp speaker show dragents with new dragent list --bgp-speaker
doc: BGP dynamic routing guide: replaced deprecated bgp speaker show dragents with new dragent list --bgp-speaker

Change-Id: Ia55757ab6dfb9eca3296b09dd0e5b2afab5811f5

mahak/neutron,openstack/neutron,mahak/neutron,openstack/neutron,openstack/neutron,mahak/neutron