net: make if_bridgevar.h self-contained

Reviewed by:	imp
Sponsored by:	Rubicon Communications, LLC ("Netgate")
Differential Revision:	https://reviews.freebsd.org/D33502

sys/net/if_bridgevar.h

@@ -76,10 +76,14 @@
  * Data structure and control definitions for bridge interfaces.
  */
 
+#include <sys/types.h>
 #include <sys/callout.h>
 #include <sys/queue.h>
 #include <sys/condvar.h>
 
+#include <net/ethernet.h>
+#include <net/if.h>
+
 /*
  * Commands used in the SIOCSDRVSPEC ioctl.  Note the lookup of the
  * bridge interface itself is keyed off the ifdrv structure.