bug#60416: Be more liberal using copy_file_range() with NFS mounted filesystems

[Braiam]

When using a nfs export, cp seems to not try hard enough using
copy_file_range(). This was
the conclusion we arrived in this forum thread[1] at Truenas forums.
It was found a way to force
cp to use it, but it should not be necessary, since there are supposed
to be fallbacks.

I'm unsure if we found something that triggered the undesired behavior.

[1]: 
https://www.truenas.com/community/threads/nfs-does-not-support-server-side-copy-with-zfs.103309/post-712071

-- 
Braiam