add {active,N} socket option for TCP, UDP, and SCTP

Add the {active,N} socket option, where N is an integer in the range
-32768..32767, to allow a caller to specify the number of data messages to
be delivered to the controlling process. Once the socket's delivered
message count either reaches 0 or is explicitly set to 0 with
inet:setopts/2 or by including {active,0} as an option when the socket is
created, the socket transitions to passive ({active, false}) mode and the
socket's controlling process receives a message to inform it of the
transition. TCP sockets receive {tcp_passive,Socket}, UDP sockets receive
{udp_passive,Socket} and SCTP sockets receive {sctp_passive,Socket}.

The socket's delivered message counter defaults to 0, but it can be set
using {active,N} via any gen_tcp, gen_udp, or gen_sctp function that takes
socket options as arguments, or via inet:setopts/2. New N values are added
to the socket's current counter value, and negative numbers can be used to
reduce the counter value. Specifying a number that would cause the socket's
counter value to go above 32767 causes an einval error. If a negative
number is specified such that the counter value would become negative, the
socket's counter value is set to 0 and the socket transitions to passive
mode. If the counter value is already 0 and inet:setopts(Socket,
[{active,0}]) is specified, the counter value remains at 0 but the
appropriate passive mode transition message is generated for the socket.

This commit contains a modified preloaded prim_inet.beam due to changes in
prim_inet.erl.

Add tests for {active,N} mode for TCP, UDP, and SCTP sockets.

Add documentation for {active,N} mode for inet, gen_tcp, gen_udp, and
gen_sctp.

1 files changed, 13 insertions, 4 deletions

diff --git a/lib/kernel/doc/src/gen_udp.xml b/lib/kernel/doc/src/gen_udp.xml
index faca31e928..503725fe18 100644
--- a/lib/kernel/doc/src/gen_udp.xml
+++ b/lib/kernel/doc/src/gen_udp.xml
@@ -145,14 +145,23 @@
               <seealso marker="inet#setopts/2">inet:setopts/2</seealso>.</p>
           </item>
         </taglist>
-        <p>The returned socket <c><anno>Socket</anno></c> is used to send packets
-          from this port with <c>send/4</c>. When UDP packets arrive at
-          the opened port, they are delivered as messages:</p>
+        <p>The returned socket <c><anno>Socket</anno></c> is used to send
+          packets from this port with <c>send/4</c>. When UDP packets arrive
+          at the opened port, if the socket is in an active mode the packets
+          are delivered as messages to the controlling process:</p>
         <code type="none">
 {udp, Socket, IP, InPortNo, Packet}</code>
-        <p>Note that arriving UDP packets that are longer than
+        <p>If the socket is not in an active mode, data can be
+          retrieved via the <seealso marker="#recv/2">recv/2,3</seealso> calls.
+          Note that arriving UDP packets that are longer than
           the receive buffer option specifies, might be truncated
           without warning.</p>
+        <p>When a socket in <c>{active, N}</c> mode (see <seealso marker="inet#setopts/2">
+          inet:setopts/2</seealso> for details) transitions to passive
+          (<c>{active, false}</c>) mode, the controlling process is notified by a
+          message of the following form:</p>
+        <code type="none">
+{udp_passive, Socket}</code>
         <p><c>IP</c> and <c>InPortNo</c> define the address from which
           <c>Packet</c> came. <c>Packet</c> is a list of bytes if
           the option <c>list</c> was specified. <c>Packet</c> is a