L2ARC: Cleanup buffer re-compression

When compressed ARC is disabled, we may have to re-compress when
writing into L2ARC. If doing so we can't fit it into the original
physical size, we should just fail immediately, since even if it
may still fit into allocation size, its checksum will never match.

While there, refactor the code similar to other compression places
without using abd_return_buf_copy().

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes #16038