MFC r301754,r301769:

r301754 (by pfg):

libc/rpc: Make use of some xdr_* macros.

xdr_rpcprog and xdr_rpcvers were broken in older versions of FreeBSD
but were fixed in r296394. Give them some use hoping they help make
the code somewhat more readable.

r301769 (by pfg):

libc/rpc: Make use of some xdr_* macros. (part 2)

xdr_rpcproc, xdr_rpcprog and xdr_rpcvers were broken in older
versions of FreeBSD but fixed in r296394. Give them some use
hoping they help make the code somewhat more readable.