linuxkpi: Migrate to IfAPI

Summary:
Trivial changes for LinuxKPI to use IfAPI.  The 'bsdifp' looks unused,
so removed it instead of converting it to a pointer.

Bump __FreeBSD_version for change to struct net_device.

Reviewed by:	bz, hselasky
Sponsored by:	Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D39491

sys/compat/linuxkpi/common/include/linux/if_vlan.h

@@ -44,7 +44,7 @@
 static inline int
 is_vlan_dev(struct ifnet *ifp)
 {
-	return (ifp->if_type == IFT_L2VLAN);
+	return (if_gettype(ifp) == IFT_L2VLAN);
 }
 
 static inline uint16_t

sys/compat/linuxkpi/common/include/linux/netdevice.h

@@ -106,9 +106,6 @@ struct net_device_ops {
 };
 
 struct net_device {
-	/* BSD specific for compat. */
-	struct ifnet			bsdifp;
-
 	/* net_device fields seen publicly. */
 	/* XXX can we later make some aliases to ifnet? */
 	char				name[IFNAMSIZ];

sys/sys/param.h

@@ -76,7 +76,7 @@
  * cannot include sys/param.h and should only be updated here.
  */
 #undef __FreeBSD_version
-#define __FreeBSD_version 1400087
+#define __FreeBSD_version 1400088
 
 /*
  * __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,