Refactor Netlink into FIB and Netlink module (#177)

examples/fib/main.go

examples/fib/main_ipv4.go

examples/fib/main_ipv6.go

go.mod

protocols/device/server_darwin.go

protocols/fib/fib.go

protocols/fib/fib_linux.go

protocols/fib/fib_linux_test.go

protocols/fib/reader_linux.go

protocols/fib/writer_linux.go

route/fib_path.go

route/path.go

route/path_test.go

route/route.go

route/route_test.go