socket: move frame params struct mnl_ring from mnl_socket

And mnl_socket_ring() requires struct nl_mmap_req for each
of TX/RX ring.
socket: introduce MNL_RING_MSGHDR macro
socket: introduce mnl_socket_poll_rx
nlmsg: introduce mnl_nlmsg_batch_reset_buffer for mmap
examples: update for mnl_socket_set_ring change
examples: update using MNL_RING_MSGHDR
examples: update for mnl_socket_poll_rx
examples: separate mmap
examples: add for mmap exclude rtnl