Check for RAID10 in set_avail_alloc_bits

Check for RAID10 in set_avail_alloc_bits

When raid is setup with mkfs, it is supposed to cow the initial filesystem
it creates up to the desired raid level.  RAID10 was not in the list
of RAID levels it checked for, so the initial FS created for RAID10
actually only lived on the first disk.

This works well enough because all the roots get quickly cowed during the
first mount.  The exception is the data relocation tree, which only gets
cowed when we do a balance.

Signed-off-by: Chris Mason <chris.mason@oracle.com>