unionfs: better handling when copying up permissions

unionfs: better handling when copying up permissions

When we copyup a file, directory, or symlink, we may be copying up from one
file system type to another.  The destination file system may not support
all of the features of the source file system, and the differences in
support may be minor.  For example jffs2 doesn't allow one to chmod a
symlink (and it returns a -EOPNOTSUPP).  So we ignore such harmless errors,
rather than propagating them up, which results in copyup errors and errors
returned back to users.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>