fix Mac build error

[zhangxp1998]

#85

Looks like there's some rename error in libpnet_bandwhich_fork? Not totally sure. The build is broken on Mac.
anyway I just found that we could fix the dependency problem without renaming, by adding these 2 lines to Cargo.toml:

[patch.crates-io]
pnet = { git = "https://github.com/zhangxp1998/libpnet.git", branch = 'bandwhich'}

This way we don't have to rename the bandwhich codebase or our fork of libpnet