Fix an overflow bug in the blist allocator that needlessly capped max

Fix an overflow bug in the blist allocator that needlessly capped max
swap size by dividing a value, which was always a multiple of 64, by
64.  Remove the code that reduced max swap size down to that cap.

Eliminate the distinction between BLIST_BMAP_RADIX and
BLIST_META_RADIX.  Call them both BLIST_RADIX.

Make improvments to the blist self-test code to silence compiler
warnings and to test larger blists.

Reported by:	jmallett
Reviewed by:	alc
Discussed with:	kib
Tested by:	pho
Differential Revision:	https://reviews.freebsd.org/D25736