Commit 947bd2479b added support for the Secinfo_no_name operation.
When a non-exported file system is being traversed, the list of
security flavors is empty. It turns out that the Linux client
mount attempt fails when the security flavors list in the
Secinfo_no_name reply is empty.
This patch modifies Secinfo/Secinfo_no_name so that it replies
with all four security flavors when the list is empty.
This fixes Linux NFSv4.1/4.2 mounts when the file system at
the NFSv4 root (as specified on a V4: exports(5) line) is
not exported.
MFC after: 2 weeks
56e9d8e38e