cam(4): preserve alloc_flags when copying CCBs

cam(4): preserve alloc_flags when copying CCBs

Before UMA CCBs, all CCBs were of the same size, and could
be trivially copied using bcopy(9).  Now we have to preserve
alloc_flags, otherwise we might end up attempting to free
stack-allocated CCB to UMA; we also need to take CCB size
into account.

This fixes kernel panic which would occur when trying to access
a stopped (as in, SCSI START STOP, also "ctladm stop") SCSI device.

Reported By:	Gary Jennejohn <gljennjohn@gmail.com>
Tested By:	Gary Jennejohn <gljennjohn@gmail.com>
Reviewed By:	imp
Sponsored by:	NetApp, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D31054