[bgp][service] Start bgp service after interfaces-config service (#11827)

- Why I did it
interfaces-config service restarts networking service, during the restart loopback interface address is being removed and reassigned back, leaving loopback without an ipv4 address for a while.
On SONiC startup and config reload interfaces-config and bgp services start in parallel and sometimes
fpmsyncd in bgp attempts bind to loopback while it does not have an address, fails with the log
Exception "Cannot assign requested address" had been thrown in daemon
and exits with rc 0.

root@sonic:/# supervisorctl status
fpmsyncd                         EXITED    Jul 20 05:04 AM
zebra                            RUNNING   pid 35, uptime 6:15:05
zsocket                          EXITED    Jul 20 05:04 AM
docker logs bgp
INFO exited: fpmsyncd (exit status 0; expected)
With fpmsyncd dead, configured routes do not appear in the database.

- How I did it
Added ordering dependency on interfaces-config service into bgp.config

- How to verify it
Itself the issue reproduces quite rarely, but one can gain the time interval between networking down and networking up in interfaces-config.sh like this:

diff --git a/files/image_config/interfaces/interfaces-config.sh b/files/image_config/interfaces/interfaces-config.sh
index f6aa4147a..87caceeff 100755
--- a/files/image_config/interfaces/interfaces-config.sh
+++ b/files/image_config/interfaces/interfaces-config.sh
@@ -63,7 +63,11 @@ done
 # Read sysctl conf files again
 sysctl -p /etc/sysctl.d/90-dhcp6-systcl.conf

-systemctl restart networking
+# systemctl restart networking
+
+systemctl start networking
+sleep 10
+systemctl stop networking

 # Clean-up created files
 rm -f /tmp/ztp_input.json /tmp/ztp_port_data.json
with this change the issue reproduces on every config reload.

Signed-off-by: Volodymyr Boyko <volodymyrx.boiko@intel.com>

files/build_templates/per_namespace/bgp.service.j2

@@ -7,6 +7,7 @@ After=updategraph.service
 BindsTo=sonic.target
 After=sonic.target
 Before=ntp-config.service
+After=interfaces-config.service
 StartLimitIntervalSec=1200
 StartLimitBurst=3