socket_mcjoin6 - join a multicast group

       socket_mcjoin6 joins the IPv6 multicast group groupip on interface.

       If something goes wrong, socket_mcjoin6 returns -1, setting errno appropriately.

       socket_mcjoin6 - join a multicast group

socket_mcleave6(3), socket_mcjoin4(3), socket_getifidx(3)

                                                                                               socket_mcjoin6(3)

#include<libowfat/socket.h>

       int socket_mcjoin6(int s,const char groupip[16],uint32 interface);