[show] Fix show arp in case with FDB entries, linked to default VLAN (#1357)

* Adding condition to check result of getting of Vlan id, using bvid.
  If the vlan id is None, then skip the record to avoid exception raising on int(NoneType)

Signed-off-by: Maksym Belei <[email protected]>

Author: maksymbelei95

scripts/nbrshow

@@ -95,6 +95,10 @@ class NbrBase(object):
             elif 'bvid' in fdb:
                 try:
                     vlan_id = port_util.get_vlan_id_from_bvid(self.db, fdb["bvid"])
+                    if vlan_id is None:
+                        # the case could be happened if the FDB entry has created with linking to
+                        # default VLAN 1, which is not present in the system
+                        continue
                 except Exception:
                     vlan_id = fdb["bvid"]
                     print("Failed to get Vlan id for bvid {}\n".format(fdb["bvid"]))