refactor: remove unused header <arpa/inet.h> in protocol.cpp
refactor: remove unused header <arpa/inet.h> in protocol.cpp

Former-commit-id: 2df132cbae7bd36979e4fe0c8ca179175abfb22d
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin