g_handleattr_int() consumes the bio if the attribute matches, so when we
check bp->bio_cmd bp may have been freed. For reference, this came in
with r341275 and r341765.
Move GETATTR handling to a separate function to avoid the problem. We
do not need to set bio_completed for such bios, g_handleattr_int() will
I also removed the setting of bio_resid before the
devstat_end_transaction_bio() call. All of the md(4) bio handlers set
bio_resid already. I do not understand why we unconditionally set
bio_completed, this seems wrong if there was an I/O error.