ctrl: Don't expose write_queue in ctrl_cmd_send() api

ctrl_cmd_send() should always have taken a 'struct ctrl_connection'
as argument, not directly its write_queue member.

Let's offer a ctrl_cmd_send2() which fixes the problem, and deprecate
the old ctrl_cmd_send().

Related: OS#5751
Change-Id: Ic81af56e7ea6921ba39168727ef64c308e9c6754
diff --git a/src/ctrl/control_cmd.c b/src/ctrl/control_cmd.c
index dec19b9..db20551 100644
--- a/src/ctrl/control_cmd.c
+++ b/src/ctrl/control_cmd.c
@@ -31,6 +31,7 @@
 #include <unistd.h>
 
 #include <osmocom/ctrl/control_cmd.h>
+#include <osmocom/ctrl/control_if.h>
 
 #include <osmocom/core/msgb.h>
 #include <osmocom/core/talloc.h>
@@ -647,7 +648,7 @@
 		cmd->type = CTRL_TYPE_ERROR;
 	}
 
-	rc = ctrl_cmd_send(&cmd->ccon->write_queue, cmd);
+	rc = ctrl_cmd_send2(cmd->ccon, cmd);
 
 	talloc_free(cmd);
 	llist_del(&cd->list);