MFC: r213756

MFC: r213756
Fix the krpc so that it can handle NFSv3,UDP mounts with a read/write
data size greater than 8192. Since soreserve(so, 256*1024, 256*1024)
would always fail for the default value of sb_max, modify clnt_dg.c
so that it uses the calculated values and checks for an error return
from soreserve(). Also, add a check for error return from soreserve()
to clnt_vc.c and change __rpc_get_t_size() to use sb_max_adj instead of
the bogus maxsize == 256*1024.

git-svn-id: svn://svn.freebsd.org/base/stable/8@214415 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f