open.2: update description for O_PATH

• Add fstatfs(), fchdir(), fchroot(), extattr_*_fd(), cap_*_get(), cap_*_limit() to the list of syscalls that can take an O_PATH fd.
• Remove readlinkat() from the list, since it is already discussed in the first few lines of the paragraph. It was originally added to the list when readlinkat() adds support for non-dir fd with an empty relative path (as if with AT_EMPTY_PATH), however, such use case is also discussed in the next paragraph.
• Add funlinkat() to the list, since it accepts an extra fd (of the file to be unlinked), which is worth extra mentioning.
• Fix a syntax issue which causes a bogus space to be rendered before a closing parentheses.

Signed-off-by: CismonX <admin@cismon.net>

Reviewed by: markj, jhb
MFC after: 2 weeks
Pull Request: https://github.com/freebsd/freebsd-src/pull/1564