Repair ext2fs writes.

Strong candidate for backport to 6.x.

When allocating new blocks, the search for block group beginnings
would fail with a segfault.  There was a side-effect read access with
an off-by-one errors.  The results were not used in the error case so
the code worked in the past.  But now the FreeBSD kernel has tighter
mappings and the word accessed is not mapped (for me).

The Linux kernel has rewritten most of the allocation strategy by now.
Also, the Linux kernel cleaned up the integration of these files and
it look feasable to wrap the original Linux files in wrapper that
provides their favorite arguments instead of dragging around our own
code.

sys/gnu/fs/ext2fs/ext2_bitops.h

@@ -88,7 +88,7 @@ find_next_zero_bit(void *data, size_t sz, size_t ofs)
 		p++;
 		ofs = (ofs + 31U) & ~31U;
 	}
-	while(*p == ~0U && ofs < sz) {
+	while(ofs < sz && *p == ~0U) {
 		p++;
 		ofs += 32;
 	}