[docker-dhcp-relay] limit privileged flag for dhcp_relay container (#…

…16817)

### Why I did it
HLD implementation: Container Hardening (sonic-net/SONiC#1364)
##### Work item tracking
- Microsoft ADO **(number only)**: 14807420

#### How I did it
Reduce linux capabilities in privileged flag

#### How to verify it
Run dhcprelay sonic-mgmt tests
Check container's settings: Privileged is false and container only has default Linux caps, does not have extended caps.
```
admin@vlab-05:~$ docker inspect dhcp_relay | grep Privilege
            "Privileged": false,
admin@vlab-05:~$ docker exec -it dhcp_relay bash
root@vlab-05:/# capsh --print
Current: cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap=ep
Bounding set =cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap
```

rules/docker-dhcp-relay.mk

@@ -45,7 +45,7 @@ endif
 endif
 
 $(DOCKER_DHCP_RELAY)_CONTAINER_NAME = dhcp_relay
-$(DOCKER_DHCP_RELAY)_CONTAINER_PRIVILEGED = true
+$(DOCKER_DHCP_RELAY)_CONTAINER_PRIVILEGED = false
 $(DOCKER_DHCP_RELAY)_CONTAINER_VOLUMES += /etc/sonic:/etc/sonic:ro
 $(DOCKER_DHCP_RELAY)_CONTAINER_VOLUMES += /etc/timezone:/etc/timezone:ro
 $(DOCKER_DHCP_RELAY)_CONTAINER_TMPFS += /tmp/