MFC kern.msgbufsize: r217688-217689,r217709,r218666-218667,r218913.

MFC kern.msgbufsize: r217688-217689,r217709,r218666-218667,r218913.
Note, that arm/{s3c2xx0,econa} exist only in head, thus not merged.

r217688:
 Make MSGBUF_SIZE kernel option a loader tunable kern.msgbufsize.

r217689:
 Add kern.msgbufsize default setting to /boot/defaults/loader.conf.

r217709,218666-218667,218913 by marcel, cognet:
 Fix up for various arm subtargets: call init_param1() before we use
 msgbufsize, now that the size of the message buffer is a tunable.

Reviewed by:	marcel
Approved by:	avg (mentor)

git-svn-id: svn://svn.freebsd.org/base/stable/8@219662 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f