Add suffix to protocol specific Socket methods

[Thomasdezeeuw]

We currently split all methods in different impl blocks with documentation to indicate what kind of socket level the method operates on, e.g. SOL_SOCKET or IPPROTO_IP.

However in some cases a socket option can be used with multiple protocols, e.g. IP_HDRINCL, this can lead to confusing error as seen in #517.

I propose we add a suffix to all not SOL_SOCKET methods. For example:

• SOL_SOCKET -> none,
• IPPROTO_IP -> _v4,
• IPPROTO_IPV6 -> _v6,
• IPPROTO_TCP -> _tcp,
• IPPROTO_UDP -> _udp.

The methods will be a bit more annoying to call, but at least it will result in less errors.

[Thomasdezeeuw]

For IPv4 this is being done in #549, for IPv6 this is already done.