During perf testing of receiving and installing 7.5 million
routes into zebra it was noticed that memset in bgp_zebra_announce
was taking ~11% of the runtime. With this change bgp_zebra_announce
now no longer has any appreciable time spent in memset as reported
by perf. In addition bgp_zebra_announce run time in perf was
reduced by a composite amount.
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>