ipn/ipnlocal: add tailnet MagicDNS name to ipn.LoginProfile

Start backfilling MagicDNS suffixes on LoginProfiles.

Updates #9286

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

types/netmap/netmap.go

@@ -171,6 +171,9 @@ func MagicDNSSuffixOfNodeName(nodeName string) string {
 //
 // It will neither start nor end with a period.
 func (nm *NetworkMap) MagicDNSSuffix() string {
+	if nm == nil {
+		return ""
+	}
 	return MagicDNSSuffixOfNodeName(nm.Name)
 }