Further cleanup to the native parts of libnet/libnio

The SAP development team has done several minor fixes and adoptions to libnet/libnio which seem worthwile contributing. In detail these are:
- unify definition of union type "SOCKETADDRESS" between windows/unix implementations
- move declaration of function NET_Wait to net_util.h as it is implemented/used for both, windows/unix
- remove function NET_AllocSockaddr
- remove definitions of SOCKADDR_LEN, SOCKETADDRESS_LEN, just rely on sizeof(SOCKETADDRESS)
- add some further initializations of variables
- formatting cleanups
- minor other fixes