We explicitly track bluefs extents in the bluefs_extents
interval_set stored in the superblock.  Telling the
freelist about it is redundant.  It's also slow, because
bluefs uses a bit portion of the device and the bitmap
representation has to flip a lot of bits in the KV store
during mkfs (or possibly during a freespace balance).

Signed-off-by: Sage Weil <sage@redhat.com>

In init_add_free we only use the min_alloc_size aligned
portion of the provided extent.  Since we have some
callers that add in free space and then take it back,
make init_rm_free do the same.  That way we can, e.g,
init_add_free 0x1000~0x400000000 (alloc will add
0x10000~0x3ffffff0000) and then
init_rm_free 0x1000~0x100000 (alloc will remove
0x10000~0xf0000).

Signed-off-by: Sage Weil <sage@redhat.com>

The only other instance of FreelistManager defines this
differently anyway.

Signed-off-by: Sage Weil <sage@redhat.com>