[kernel|test|gen-udp] Add explicit open test case
[kernel|test|gen-udp] Add explicit open test case

Add test case that explicitly opens a UDP socket with the
add_mebership option.

OTP-18323

bjorng/otp,bjorng/otp,bjorng/otp,bjorng/otp,bjorng/otp,erlang/otp,erlang/otp,bjorng/otp,erlang/otp,erlang/otp,bjorng/otp,erlang/otp,bjorng/otp,bjorng/otp,erlang/otp,erlang/otp,erlang/otp,erlang/otp,bjorng/otp,erlang/otp