Fixes netifgen

This was a problem from back in plan9, which I fixed in our NxM port.

The root issue is that netif code can't tell the difference between a
QID with a netid of 0 and one with no netid at all.  I think I fixed it.
I left in my comments for the next time we need to debug this.
Dev zeros the dir path before genning

It's useful for devices to be able to get information about the last run
through their gen function when run in a tight loop.  There's no good
way to do pass an arbitrary value back, but we can use the dir to
communicate the result of the previous run.  So long as we handle the
initial case.

Gens communicate via the dir, and dir->qid.path is the last path used in
the previous run.  This works if we can bootstrap it, and passing in
gibberish (on the stack) or ancient versions of dir will mess things up.
So now any caller of a gen in a loop will make sure dir's path is 0.

Also, it's not sufficient to just check for {s,i} == 0 to detect the
"first run" of a gen.  Sometimes (devdirread()), a device will be asked
to gen starting at a higher value of its iterator.  By zeroing dir's
path, a gen can tell if it is in the middle or not of a series of runs.
Moved devtab and dev to k/s/ns

They aren't really devices, just support stuff.
Adds chaninfo()

This is useful for debugging.  Most devices will use devchaninfo.  But
if you want to spit out extra info, take a look at ipchaninfo.

This info will show up now when we do a "procinfo pid #" from the kernel
monitor.  We could also use it from procfs in the future.
Fixes a few warnings and printfmt %i

The warning was hiding the wrong order of hnputl.  Hopefully this does
what we want.  =)

I also commented out the mii.c, which we're not using right now.
Makes mount slightly more useful

Couldn't pass more than one flag (e.g. -a and -c).