Make shmif buildable when DRPINTF enabled

use _KERNEL_RCSID only in _KERNEL, _RCSID elsewhere

header massage, mostly improves portability

Update copyright statements.

no functional change.

make this happy to compile standalone

Fix hopefully last off-by-one: if we fill the bus, we must also
advance the "first" pointer. This problem triggered only if the
bus was filled in the first round, since the first pointer is at
the e

Fix hopefully last off-by-one: if we fill the bus, we must also
advance the "first" pointer. This problem triggered only if the
bus was filled in the first round, since the first pointer is at
the end-of-bus only for the bootstrap round.

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* fix off-by-wrap case where current datagram aligns exactly with
the end of the bus
* clarify the "can we still use the device's next pointer" calculation
and move it to its own routine
* sprink

* fix off-by-wrap case where current datagram aligns exactly with
the end of the bus
* clarify the "can we still use the device's next pointer" calculation
and move it to its own routine
* sprinkle dprintf

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simplify, improve, etc.

Move the lockops together with the interface -- they are needed
only at runtime.

introduce a sleep to trying to grab the bus

Include a timestamp in the frame header. When converting to pcap,
it can give some idea of when packets were sent.

nb. it's the sending host's timestamp, not an observer timestamp
like in the typic

Include a timestamp in the frame header. When converting to pcap,
it can give some idea of when packets were sent.

nb. it's the sending host's timestamp, not an observer timestamp
like in the typical pcap case.

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Include a pointer to the beginning of the buffer and add support
to the packet dumper. This helps in situations where the juicy
details are in a bus multiple generations old.