roken: do not override system network address functions

Roken functions rk_copyhostent(), rk_freeaddrinfo(), rk_freehostent()
rk_getaddrinfo(), rk_getipnodebyaddr(),  rk_getipnodebyname(), and
rk_getnameinfo() should never be built without the "rk_" prefix.  Doing
so overrides the system provided functions of the same name when they
exist.

lib/roken/getipnodebyaddr.c

@@ -41,7 +41,7 @@
  */
 
 ROKEN_LIB_FUNCTION struct hostent * ROKEN_LIB_CALL
-getipnodebyaddr (const void *src, size_t len, int af, int *error_num)
+rk_getipnodebyaddr(const void *src, size_t len, int af, int *error_num)
 {
     struct hostent *tmp;