* sysdeps/mach/hurd/readlink.c (__readlink): Don't clobber original
LEN value with io_read result; save it and compare them just in case
the server bogusly returns more than we asked for.
* sysdeps/mach/hurd/recv.c (recv): Likewise for socket_recv.
* sysdeps/mach/hurd/recvfrom.c (recvfrom): Likewise.
* hurd/fd-read.c (_hurd_fd_read): Likewise for io_read.
Initialize NREAD before the RPC. I think this must only have failed
to bomb before because all the servers always return ool data(?).