bgpd: Properly use bgp_path_info_cmp for evpn usage

bgpd: Properly use bgp_path_info_cmp for evpn usage

Currently evpn passes into bgp_path_info_cmp the pfx_buf
uninitialized.  The bgp_path_info_cmp functionality actually
expects this value to be initialized.  Additionally the
evpn section of bgp_path_info_comp was resetting the
new_buf and exist_buf values that were already being
set above to the same values if !debug was on( which
precluded it ever from happening )

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