Remove Git dependency on netmap_sys
Remove Git dependency on netmap_sys

This hopefully will allow publishing the new version on crates.io.

little-dude/libpnet,symphorien/libpnet,symphorien/libpnet,symphorien/libpnet,mrmonday/libpnet,mrmonday/libpnet,libpnet/libpnet,fsck/libpnet,mrmonday/libpnet,libpnet/libpnet,returntoreality/libpnet,returntoreality/libpnet,fsck/libpnet,tempbottle/libpnet,libpnet/libpnet,fsck/libpnet,libpnet/libpnet,fsck/libpnet,tempbottle/libpnet,little-dude/libpnet,little-dude/libpnet,tempbottle/libpnet,tempbottle/libpnet,little-dude/libpnet,returntoreality/libpnet,mrmonday/libpnet,returntoreality/libpnet,symphorien/libpnet