Router objects with BGP enabled are incorrectly validated when used on multiple DPs

[gizmoguy]

When a check_config() is called on a Router object, the type of neighbor_addresses and server_addresses changes from list to frozenset:

    def check_config(self):
.....
            for field in self.ipaddress_fields:
                if field in self.bgp:
                    self.bgp[field] = frozenset([
                        self._check_ip_str(ip_str) for ip_str in self.bgp[field]])

This trips up if check_config() is called again on the same Router object:

[InvalidConfigError("DP swdev: server_addresses value frozenset({IPv4Address('127.0.0.1')}) must be <class 'list'> not <class 'frozenset'>")]

A terrible fix could be updating the type when we encapsulate it in frozenset() but it seems like there could be a better fix:

diff --git a/faucet/router.py b/faucet/router.py
index 4b6b44ce..33acb6cd 100644
--- a/faucet/router.py
+++ b/faucet/router.py
@@ -84,6 +84,7 @@ class Router(Conf):
                 if field in self.bgp:
                     self.bgp[field] = frozenset([
                         self._check_ip_str(ip_str) for ip_str in self.bgp[field]])
+                    self.bgp_defaults_types[field] = frozenset
             for accessor_val, required_field in (
                     (self.bgp_ipvs(), 'server_addresses'),
                     (self.bgp_as(), 'as'),