Hardware checksums on bge(4) interfaces

[Chris Ross <cross+netbsd%distal.com@localhost>]

  Just a question.  Is there any reason *not* to use the various pieces 
of hardware checksumming that are shown as available on my bge(4) 
interfaces?  Each of them show bidirectional IP, TCP, and UDP checksum 
capabilities.  But, they're not enabled by default.  I would've expected 
that they'd just *always* be valuable, but they're not automatically 
enabled, so I was wondering what the reasons would be to turn them on, 
to leave them turned off, etc.

  Sorry if this should be a tech-net question, but it is really meant 
to be pretty inspecific and open.  Thanks.

                                                        - Chris

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Chris Ross