Revert "VFS: Remove VV_READLINK flag" and "fdescfs: improve linrdlnk mount option"

This reverts commits 4a402dfe0bc44770c9eac6e58a501e4805e29413 and
3bffa2262328e4ff1737516f176107f607e7bc76.

The fix will be implemented in somewhat different manner. The semantic
adjustment is incompatible with linuxolator expectations.

Reported and reviewed by: dchagin
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D40969