As with gzip, let the dump device be smaller than physical memory
when using zstd and full dumps.
Also print the error message if the size check fails, even if -v
is not specified. Failing silently is not friendly.
Reviewed by: cem markj
MFC after: 2 weeks
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D23923
7bef70737b