Fixed: RPi freezes during boot from SD-card.

[Ralf Wenk]

Hi,

just in case somebodys RPi freezes during multiuser boot from SD-Card
between r249940 and r250708 after printing "Mounting local file systems:"
(last command is rmdir /var/.diskless) as mine did:

The setting of d_delmaxsize in sys/dev/mmc/mmcsd.c since r250709 fixes it
here. 

r249940 introduces[1] the use of d_maxsize as default value for d_delmaxsize
if d_delmaxsize is 0 in sys/geom/geom_disk.c. With just setting d_delmaxsize
as in r250709 even r249940 does not freeze any more.

Ralf