tun/tap: merge and rename to `tuntap`

tun(4) and tap(4) share the same general management interface and have a lot
in common. Bugs exist in tap(4) that have been fixed in tun(4), and
vice-versa. Let's reduce the maintenance requirements by merging them
together and using flags to differentiate between the three interface types
(tun, tap, vmnet).

This fixes a couple of tap(4)/vmnet(4) issues right out of the gate:
- tap devices may no longer be destroyed while they're open [0]
- VIMAGE issues already addressed in tun by kp

[0] emaste had removed an easy-panic-button in r240938 due to devdrn
blocking. A naive glance over this leads me to believe that this isn't quite
complete -- destroy_devl will only block while executing d_* functions, but
doesn't block the device from being destroyed while a process has it open.
The latter is the intent of the condvar in tun, so this is "fixed" (for
certain definitions of the word -- it wasn't really broken in tap, it just
wasn't quite ideal).

ifconfig(8) also grew the ability to map an interface name to a kld, so
that `ifconfig {tun,tap}0` can continue to autoload the correct module, and
`ifconfig vmnet0 create` will now autoload the correct module. This is a
low overhead addition.

(MFC commentary)

This may get MFC'd if many bugs in tun(4)/tap(4) are discovered after this,
and how critical they are. Changes after this are likely easily MFC'd
without taking this merge, but the merge will be easier.

I have no plans to do this MFC as of now.

Reviewed by:	bcr (manpages), tuexen (testing, syzkaller/packetdrill)
Input also from:	melifaro
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D20044

1 files changed, 1 insertions, 2 deletions

diff --git a/sys/modules/Makefile b/sys/modules/Makefile
index 2c4a8047f3e4..83bbdad7c615 100644
--- a/sys/modules/Makefile
+++ b/sys/modules/Makefile
@@ -163,8 +163,7 @@ SUBDIR=	\
 	if_lagg \
 	${_if_ndis} \
 	${_if_stf} \
-	if_tap \
-	if_tun \
+	if_tuntap \
 	if_vlan \
 	if_vxlan \
 	iflib \