Low-level bindings for the [libntirpc](https://github.com/nfs-ganesha/ntirpc)
library.
Some documentation for the libary can be found in the Linux man pages
[rpc(3)](https://linux.die.net/man/3/rpc) and
[xdr(3)](https://linux.die.net/man/3/xdr). However, the doc has some
inconsistency with the library, so we should use the doc as a reference not as a
definitive guide.
Its implementation is adapted from the
[libtirpc-sys](https://crates.io/crates/libtirpc-sys) library.