Fix port leaking after controlling_process(Port, self())

Add case to handle the situation when someone call
{gen_tcp,gen_udp}:controlling_process(Port, self()). Also improve spec
and doc from gen_udp and gen_sctp for controlling_process/2.

To reproduce the issue, open an UDP port:

4> {ok,Port} = gen_udp:open(9000, [binary]).
{ok,#Port<0.587>}
5> gen_udp:controlling_process(Port, self()).
ok

Simulate error:

6> 1=2.
** exception error: no match of right hand side value 2

Here is the leak:

7> inet:i().
Port Module   Recv Sent Owner    Local Address Foreign Address State
Type
581  inet_udp 0    0    <0.31.0> *:cslistener  *:*             BOUND
DGRAM
ok

5 files changed, 14 insertions, 6 deletions

diff --git a/lib/kernel/doc/src/gen_tcp.xml b/lib/kernel/doc/src/gen_tcp.xml
index 8a5d40bb16..27c454afba 100644
--- a/lib/kernel/doc/src/gen_tcp.xml
+++ b/lib/kernel/doc/src/gen_tcp.xml
@@ -297,7 +297,7 @@ do_recv(Sock, Bs) ->
           <c><anno>Socket</anno></c>. The controlling process is the process which
           receives messages from the socket. If called by any other
           process than the current controlling process,
-          <c>{error, eperm}</c> is returned.</p>
+          <c>{error, not_owner}</c> is returned.</p>
       </desc>
     </func>
     <func>
diff --git a/lib/kernel/doc/src/gen_udp.xml b/lib/kernel/doc/src/gen_udp.xml
index daa9b7d887..9882d3fab1 100644
--- a/lib/kernel/doc/src/gen_udp.xml
+++ b/lib/kernel/doc/src/gen_udp.xml
@@ -136,7 +136,9 @@
       <desc>
         <p>Assigns a new controlling process <c><anno>Pid</anno></c> to
           <c><anno>Socket</anno></c>. The controlling process is the process which
-          receives messages from the socket.</p>
+          receives messages from the socket. If called by any other
+          process than the current controlling process,
+          <c>{error, not_owner}</c> is returned.</p>
       </desc>
     </func>
     <func>
diff --git a/lib/kernel/src/gen_sctp.erl b/lib/kernel/src/gen_sctp.erl
index d8954f0cf7..8fa963ec78 100644
--- a/lib/kernel/src/gen_sctp.erl
+++ b/lib/kernel/src/gen_sctp.erl
@@ -425,9 +425,10 @@ error_string(X) ->
     erlang:error(badarg, [X]).
 
 
--spec controlling_process(Socket, Pid) -> ok when
+-spec controlling_process(Socket, Pid) -> ok | {error, Reason} when
       Socket :: sctp_socket(),
-      Pid :: pid().
+      Pid :: pid(),
+      Reason :: closed | not_owner | inet:posix().
 
 controlling_process(S, Pid) when is_port(S), is_pid(Pid) ->
     inet:udp_controlling_process(S, Pid);
diff --git a/lib/kernel/src/gen_udp.erl b/lib/kernel/src/gen_udp.erl
index 8688799ae9..914854c65c 100644
--- a/lib/kernel/src/gen_udp.erl
+++ b/lib/kernel/src/gen_udp.erl
@@ -185,9 +185,10 @@ connect(S, Address, Port) when is_port(S) ->
 	    Error
     end.
 
--spec controlling_process(Socket, Pid) -> ok when
+-spec controlling_process(Socket, Pid) -> ok | {error, Reason} when
       Socket :: socket(),
-      Pid :: pid().
+      Pid :: pid(),
+      Reason :: closed | not_owner | inet:posix().
 
 controlling_process(S, NewOwner) ->
     inet:udp_controlling_process(S, NewOwner).
diff --git a/lib/kernel/src/inet.erl b/lib/kernel/src/inet.erl
index 49f64a9236..3356fb55d7 100644
--- a/lib/kernel/src/inet.erl
+++ b/lib/kernel/src/inet.erl
@@ -1244,6 +1244,8 @@ udp_close(S) when is_port(S) ->
 %% Set controlling process for TCP socket.
 tcp_controlling_process(S, NewOwner) when is_port(S), is_pid(NewOwner) ->
     case erlang:port_info(S, connected) of
+	{connected, NewOwner} ->
+	    ok;
 	{connected, Pid} when Pid =/= self() ->
 	    {error, not_owner};
 	undefined ->
@@ -1295,6 +1297,8 @@ tcp_sync_input(S, Owner, Flag) ->
 %% Set controlling process for UDP or SCTP socket.
 udp_controlling_process(S, NewOwner) when is_port(S), is_pid(NewOwner) ->
     case erlang:port_info(S, connected) of
+	{connected, NewOwner} ->
+	    ok;
 	{connected, Pid} when Pid =/= self() ->
 	    {error, not_owner};
 	_ ->