Gone serial console on rpi3

[bob prohaska]

Lately it seems the serial console on my Pi3 has gone
missing. It's up and working for u-boot and loader, 
but once the kernel comes up the serial console falls
silent. First noticed about two weeks ago. 

Backing down to an old kernel doesn't seem to help,
as if something changed in userland. It appears that my
userland was corrupted by a USB flash during make installworld,
so lots of other things aren't working also... For now
I'm trying to dig myself out of that hole.

IIRC nothing special was needed to turn on the serial
console, if that's changed please clue me in.

On the plus side, single user mode now works with the
USB keyboard, which is a great help.

Thanks for reading,

bob prohaska