fix getdirentries man page for NFS client returning d_off == 0

[rmacklem]

Summary

PR3253428 reported that getdirentries(2) was
returning dirents with d_off set to 0 for an NFS
mount.

This is believed to be correct behaviour at
this time (it may change for some NFS mounts
in the future), but is inconsistent with what the
getdirentries(2) man page says.

This patch fixes the man page.

[asomers]

lib/libc/sys/getdirentries.2

95

I find this confusing. Is the antecedent of "it" "cookie", "directory descriptor", or "entry"? I would say "returns a cookie which, if non-zero, can be used with lseek to position the directory descriptor to the next entry."

151

I would shorten this to "if non-zero".

[rmacklem]

Apply changes suggested by asomers@.

[rmacklem]

Marked inline comments as done.

[asomers]

Approved, but you should fix the bug number in the commit message.