MFC: r281960

MFC: r281960
MAXBSIZE defines both the largest UFS block size and the
largest size for a buffer in the buffer cache. This patch
defines a new constant MAXBCACHEBUF, which is the largest
size for a buffer in the buffer cache. Having a separate
constant allows MAXBCACHEBUF to be set larger than MAXBSIZE
on a per-architecture basis, so that NFS can do larger read/writes
for these architectures. It modifies sys/param.h so that BKVASIZE
can also be set on a per-architecture basis.
A couple of cases where NFS used MAXBSIZE instead of NFS_MAXBSIZE
is fixed as well.

git-svn-id: svn://svn.freebsd.org/base/stable/10@282933 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f