[CFR] a small change of ifconfig(8)

Hello all,

I'm sending this email to check whether my approach is reasonable that I
added 2 line into ifconfig(8) to skip IFT_USB interfaces as follows:

+		if (sdl != NULL && sdl->sdl_type == IFT_USB)
+			continue;

And as additionally I added two changes of USB pf to call if_up(ifp) /
if_down(ifp) explicitly to UP usbus interfaces though normally it always
should be called through user ioctl calls.

The reason why I make this patch is that I encountered a side-effect
output from ifconfig(8) after USB packet filter is committed.  Yes usbus
interfaces are printed.

Please give me some hints whether the patch is reasonable.  If it's
reasonable, is there other tools which I should make patches?

regards,
Weongyo Jeong