improve error messages (remove \n, use __func__, etc)

Fix -Wsign-compare issues.
(Use %u not %d for unsigned ints.)

some changes to serial bluetooth host controller interfaces

btuartd(8) should be named btattach(8) for consistency
with other parts of NetBSD

make btattach(8) a single-use tool for less complexity

some changes to serial bluetooth host controller interfaces

btuartd(8) should be named btattach(8) for consistency
with other parts of NetBSD

make btattach(8) a single-use tool for less complexity

device specicific initialisation (from btuart(4)) is carried
out prior to activating the line discipline (in btattach(8)),
which simplifies the API somewhat and means that the user
tool and the kernel do not need to be kept in sync.

btuart(4) driver is much reduced; naming is made consistent
and all tsleep() and delay() are removed to userland

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