ctrl: prep test: separate new ctrl_handle_msg() from handle_control_read()

In order to allow unit testing the ctrl iface msgb handling, have a separate
msgb entry point function from the actual fd read function.

An upcoming patch will prove a memory leak in CTRL msgb handling by a unit test
that needs this separation.

Change-Id: Ie09e39db668b866eeb80399b82e7b04b8f5ad7c3
diff --git a/include/osmocom/ctrl/control_if.h b/include/osmocom/ctrl/control_if.h
index d444328..5fa9588 100644
--- a/include/osmocom/ctrl/control_if.h
+++ b/include/osmocom/ctrl/control_if.h
@@ -43,3 +43,5 @@
 struct ctrl_cmd *ctrl_cmd_exec_from_string(struct ctrl_handle *ch, const char *cmdstr);
 
 int ctrl_lookup_register(ctrl_cmd_lookup lookup);
+
+int ctrl_handle_msg(struct ctrl_handle *ctrl, struct ctrl_connection *ccon, struct msgb *msg);