Replace hardcoded constants from <sys/socket.h> with FFI references
Replace hardcoded constants from <sys/socket.h> with FFI references

Guarantees that the mapped Int values are correct across platforms.
More specifically, this allows creating IPv6 sockets on macOS.

kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev