QEMU code does not work well with too big numbers on the JSON monitor so
our monitor code supports sending only numbers up to LLONG_MAX. Avoid a
weird error message by limiting the size of the 'bandwidth' parameter
for block copy.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1532542Signed-off-by: NPeter Krempa <pkrempa@redhat.com>