nacl_io: Handle missing socket options in setsockopt

This patch adds missing support for handling broadcast and multicast
options in UDP sockets. It is required to update the UDPSocket
interface to use PPB_UDPSocket_1_2, available in M43.

Refactor SocketNode, TCPNode and UDPNode so SetSockOpt() method is
available only on the parent class and each subclass thus implements
the specialized method according to the level.

BUG=None

Signed-off-by: Eduardo Lima (Etrunko) <eduardo.lima@intel.com>

Review URL: https://codereview.chromium.org/1258123002

Cr-Commit-Position: refs/heads/master@{#341572}

• AUTHORS[diff]
• native_client_sdk/src/AUTHORS[diff]
• native_client_sdk/src/libraries/nacl_io/pepper/all_interfaces.h[diff]
• native_client_sdk/src/libraries/nacl_io/socket/socket_node.cc[diff]
• native_client_sdk/src/libraries/nacl_io/socket/socket_node.h[diff]
• native_client_sdk/src/libraries/nacl_io/socket/tcp_node.cc[diff]
• native_client_sdk/src/libraries/nacl_io/socket/tcp_node.h[diff]
• native_client_sdk/src/libraries/nacl_io/socket/udp_node.cc[diff]
• native_client_sdk/src/libraries/nacl_io/socket/udp_node.h[diff]
• native_client_sdk/src/tests/nacl_io_socket_test/socket_test.cc[diff]