T7819: VPP do not override driver if it is already done

Fixes this case:

Traceback (most recent call last):
  File "/usr/libexec/vyos/services/vyos-configd", line 156, in run_script
    script.apply(c)
  File "/usr/libexec/vyos/conf_mode/vpp.py", line 613, in apply
    control_host.override_driver(
  File "/usr/lib/python3/dist-packages/vyos/vpp/control_host.py", line 138, in override_driver
    Path('/sys/module/vfio_pci/drivers/pci:vfio-pci/new_id').write_text(
  File "/usr/lib/python3.11/pathlib.py", line 1079, in write_text
    with self.open(mode='w', encoding=encoding, errors=errors, newline=newline) as f:
FileExistsError: [Errno 17] File exists

Author: sever-sever

src/conf_mode/vpp.py

@@ -742,10 +742,21 @@ def apply(config):
                         iface_config['kernel_module'] in override_drivers
                         or override_xdp_to_dpdk
                     ):
+                        bus_id = config['persist_config'][iface]['bus_id']
+                        dev_id = config['persist_config'][iface]['dev_id']
+                        desired_driver = override_drivers[k_module]
+                        # Check driver before override
+                        drv_path = Path(f'/sys/bus/{bus_id}/devices/{dev_id}/driver')
+                        if drv_path.exists():
+                            current_driver = drv_path.resolve().name
+                            # already correctly overridden
+                            if current_driver == desired_driver:
+                                continue
+
                         control_host.override_driver(
-                            config['persist_config'][iface]['bus_id'],
-                            config['persist_config'][iface]['dev_id'],
-                            override_drivers[k_module],
+                            bus_id,
+                            dev_id,
+                            desired_driver,
                         )
 
         call('systemctl daemon-reload')