access.2: Mention that lstat(2) should be used for symbolic links

access(), eaccess() and faccessat() will always dereference
symbolic links.

So add a note in the manual page, that lstat(2) should be
used in the case of symbolic links.

PR: 262895
Reviewed by: gbe, pauamma_gundo.com
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D44890

(cherry picked from commit 421025a274fb5759b3ecc8bdb30b24db830b45ae)
(cherry picked from commit f075b6113726d74342d4af15dfab60709f50b859)

Approved by: re (cperciva)