Improve hostname functions

[matthiasblaesing]

Fix wrong mapping of libc function gethostname, sethostname,
getdomainname and setdomainname. The functions are defined as:

   int getdomainname(char *name, size_t len);
   int setdomainname(const char *name, size_t len);

   int gethostname(char *name, size_t len);
   int sethostname(const char *name, size_t len);

and a C char[] maps by default to a byte[] in java.

In addition bind the winsock gethostname function:

com.sun.jna.platform.win32.Winsock2.gethostname(byte[], int)

The sethostname and setdomainname were tested manually,
as changing the hostname is a privileged operation and
is not regularly possible in unittests.

This closes #871