9pfs: improve portability to older systems

9pfs: improve portability to older systems

Small requirements on "new" features have percolated to virtio-9p-local.c.
In particular, the utimensat wrapper actually only supports dirfd = AT_FDCWD
and flags = AT_SYMLINK_NOFOLLOW in the fallback code.  Remove the arguments
so that virtio-9p-local.c will not use AT_* constants.

At the same time, fail local_ioc_getversion if the ioctl is not supported
by the host.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>