FTP: call opensocket callback properly

When the new socket is created for an active connection, it is now done
using the open socket callback.

Test case 596 was modified to run fine, although it hides the fact that
the close callback is still called too many times, as it also gets
called for closing sockets that were created with accept().

tests/data/test596

@@ -16,9 +16,10 @@ moo
 <datacheck>
 [OPEN] counter: 1
 [OPEN] counter: 2
-moo
 [CLOSE] counter: 2
+moo
 [CLOSE] counter: 1
+[CLOSE] counter: 0
 </datacheck>
 </reply>
 
@@ -43,11 +44,14 @@ ftp://%HOSTIP:%FTPPORT/596 log/ip596 activeftp
 #
 # Verify data after the test has been "shot"
 <verify>
+<strippart>
+s/^(EPRT \|1\|)(.*)/$1/
+</strippart>
 <protocol>
 USER anonymous
 PASS ftp@example.com
 PWD
-EPSV
+EPRT |1|
 TYPE I
 SIZE 596
 RETR 596