flock: use nfs4 fallback on EBADF too

The kernel regression (probably v3.4, commit 55725513) introduces a
new errno for O_RDONLY on NFS. Now it returns EBADF rather than EIO.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1078618
Signed-off-by: Karel Zak <kzak@redhat.com>