add setdomainname syscall, fix getdomainname (previously a stub)
diff --git a/include/unistd.h b/include/unistd.h
index 4f6953c..d3bb781 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -165,6 +165,7 @@
 int getdtablesize(void);
 int sethostname(const char *, size_t);
 int getdomainname(char *, size_t);
+int setdomainname(const char *, size_t);
 int setgroups(size_t, const gid_t []);
 char *getpass(const char *);
 int daemon(int, int);