Update version to 2.1.fb43

Signed-off-by: Andy Grover <agrover@redhat.com>
Improve performance when adding many backstores

The old cache code was effective for lookups, but each cache miss caused
the cache to be regenerated by reading the filesystem. This causes O(n^2)
creation times.

Now, only fetch the cache once, then keep bs_cache updated.

Signed-off-by: Andy Grover <agrover@redhat.com>
Increase MAX_LUN to 16383

255 is too low. rtslib should be ready if the kernel lun-per-tpg limit
is raised.

Signed-off-by: Andy Grover <agrover@redhat.com>