update CHANGELOG

CHANGELOG.md

@@ -23,6 +23,8 @@ FEATURES:
 IMPROVEMENTS:
 
   - commands/ssh-config: Works without a target in multi-machine envs [GH-2844]
+  - guests/freebsd: Added `config.freebsd.device` setting to set the network
+      device prefix, defaults to "em". [GH-2956]
 
 PLUGIN AUTHOR CHANGES:
 

plugins/guests/freebsd/config.rb

@@ -1,11 +1,20 @@
 module VagrantPlugins
   module GuestFreeBSD
     class Config < Vagrant.plugin("2", :config)
+      # The device prefix for network devices created by Vagrant.
+      # This defaults to "em" but can be set for example to "vtnet"
+      # for virtio devices and so on.
+      #
+      # @return [String]
       attr_accessor :device
 
       def initialize
-        @device = "em"
+        @device = UNSET_VALUE
+      end
+
+      def finalize!
+        @device = "em" if @device == UNSET_VALUE
       end
     end
   end
-end
+end