* raimo/inherit-listen-options/OTP-15824:
  The linger option is not transferred on *BSD

Removed unnecessary spec's causing dialyzer warnings.

Invalid guard tests for function sendto. It handled the,
invalid, socket address 'null'. Presumably, this was
intended for connected UDP sockets. Though, for a
connected (UDP) socket, the send function shall be used.

Its now possible to bind a socket to the (limited) broadcast
address by specifying 'broadcast' as address:

   socket:bind(Socket, broadcast)

This is *only* valid for family 'inet'.

Add testing of sending (broadcasting) to both "limited" broadcast address
and "subnet-directed" broadcast address.

OTP-15904

Add test case for the socket option bindtodevice. Also make
correction in the nif code. Used the wrong option (broadcast).
Also added more info to doc.

Note sure if this test case actually works. Set and get "works",
but the value returned by get is always "". So either we should
extend the test to made sure the bind actually has the expected
effect or... Something for a rainy day maybe...

OTP-15904

Add test case for the socket option acceptconn. Also make
minor correction (error when trying to set this option
was incorrect). Doc was also incorrect (spelled wrong).

OTP-15904

The nif code expects the socket address to be "complete",
that is all fields must exist. This was not the case for
a couple of functions, sendto, sendmsg and connect.
What was mssing was a call to 'ensure_sockaddr'.

Test: 1) Add a condition function to test if IPv6 is available
         and works.
      2) Needed to adjust a test case (actually a common function
         used in several test cases) since the socket address
	 data type has two optional fields, which we do not
	 initiate (when sending), but the nif-code does fill in.

OTP-15897