vhost-user: Don't ask for reply on postcopy mem table set

vhost-user: Don't ask for reply on postcopy mem table set

According to documentation, NEED_REPLY_MASK should not be set
for VHOST_USER_SET_MEM_TABLE request in postcopy mode.
This restriction was mistakenly applied to 'reply_supported'
variable, which is local and used only for non-postcopy case.

CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
Fixes: 9bb38019942c ("vhost+postcopy: Send address back to qemu")
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Message-Id: <20181002140947.4107-1-i.maximets@samsung.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>