vfs_shadow_copy2: fix case where snapshots are outside the share

vfs_shadow_copy2: fix case where snapshots are outside the share

Adjust the connect path to the root of the share in the snapshot,
or to the root of the snapshot if the snapshot is "inside" the
share.

This way snapshot symlink regarded as "wide links" if and only if
they point outside the snapshot or they were wide links when
the snapshot was taken.

This allows mounting the snapshots outside the share's root.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11580

Signed-off-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>