One could end up with the wrong encoding in xenocara while having a ucc

One could end up with the wrong encoding in xenocara while having a ucc
keyboard attached and /etc/kbdtype being present. The advertised
encoding of a wsmux is a bit fragile as the last attached device will
dictate it. If this happens to be a ucc keyboard, KB_US will always be
the advertised encoding as its encoding is immutable and /etc/kbdtype is
ignored.

Instead, do not advertise the encoding for ucc devices when the parent
mux queries its attached devices. However, asking the device directly
(i.e. bypassing the mux) still returns the encoding as wsconsctl(8)
would otherwise report an error.

Thanks to landry@ for the report and testing.