[BSC] Move the TX queue draining to a separate method

This way we can replace the code from one function call
to another.

src/BSCIPAConnection.st

@@ -141,10 +141,9 @@ BSCConnection subclass: BSCIPAConnection [
 
         "Drain the send queue in a new process"
         tx := [
-            [[
-                | msg |
-                msg := writeQueue next.
-                socket nextPutAllFlush: msg.
+            [
+            [
+                self runTxQueueOnce
             ] repeat.
             ] ensure: [
                 self logNotice: 'BSC TX queue lac: %1 finished' % {self lac} area: #bsc]
@@ -152,6 +151,14 @@ BSCConnection subclass: BSCIPAConnection [
 
     ]
 
+    runTxQueueOnce [
+        | msg |
+        <category: 'private'>
+
+        msg := writeQueue next.
+        socket nextPutAllFlush: msg.
+    ]
+
     send: aMsg with: aType [
         terminated = true ifTrue: [^false].