bgpd: backpressure - cleanup bgp_zebra_XX func args

bgpd: backpressure - cleanup bgp_zebra_XX func args

Since installing/withdrawing routes into zebra is going to be changed
around to be dest based in a list,
 - Retrieve the afi/safi to use based upon the dest's afi/safi
   instead of passing it in.
 - Prefix is known by the dest. Remove this arg as well

Ticket: #3390099

Signed-off-by: Donald Sharp <sharpd@nvidia.com>
Signed-off-by: Rajasekar Raja <rajasekarr@nvidia.com>