A lot of people are writing operating systems kernels in Rust, and they'll be looking for a network stack. pnet could be a choice option.

Some thoughts:

• nom implements this as a feature on their package. Compiling with the core feature means that #![no_std] compilation is supported.
• It's probably reasonable to assume support for core, alloc, and collections.
• On the other hand, assuming support for libc is not going to go well. AFAIK It's pretty much an interface to glibc, which I wouldn't expect anyone to port to their OS.