Make sure all I/O is of sector size of the dump dev. The kernel dump header
is 512 bytes and assumed that would fit in sector but will be a partial
sector on a 4Kn disk. Introducing a new function dump_write_pad that
will write out a sector with the contents of the header padded with zeros
to the size of a sector. For now assume the max size is 4096. Using
malloc to allocate memory causes issues with:
Dump map grown while dumping. Retrying...
Update savecore to deal with 4Kn dumps.
Fix mrsas(4) so dumping works and temporarily fix mrsas(4) to boot
by removing the tsleep and replace it with DELAY in mrsas_complete_cmd
so booting doesn't hang.