fix non canonical format of IPv6 address string in bgpcfgd

IPv6 addresses text used in cfgdb may not follow the canonical IPv6 text format.
When performing IPv6 addresses equivalent check with string, need to make sure
that both of them are in the shortest form defined in rfc 5952

src/sonic-bgpcfgd/bgpcfgd/managers_bgp.py

@@ -336,6 +336,15 @@ def get_local_interface(self, local_addr):
                  If the interface has not been set, return None
         """
         local_addresses = self.directory.get_slot("LOCAL", "local_addresses")
+
+        # Handle local_addr string that is not represented in canonical text format, especially for IPv6 addresses
+        try:
+            ip = netaddr.IPAddress(str(local_addr))
+        except (netaddr.NotRegisteredError, netaddr.AddrFormatError, netaddr.AddrConversionError):
+            log_warn("IP Address '%s' format is wrong" % (local_addr))
+            return None
+        local_addr = str(ip)
+
         # Check if the local address of this bgp session has been set
         if local_addr not in local_addresses:
             return None