We don't check the direction, so don't support setting it.

If there's a direction indicator in the packets we get, we should allow
the direction to be set and should check it if it's "incoming only" or
"outgoing only".  Otherwise, we shouldn't allow the direction to be set.
diff --git a/pcap-bt-monitor-linux.c b/pcap-bt-monitor-linux.c
index 3432d32..7b75b5c 100644
--- a/pcap-bt-monitor-linux.c
+++ b/pcap-bt-monitor-linux.c
@@ -155,13 +155,6 @@
 }
 
 static int
-bt_monitor_setdirection(pcap_t *p, pcap_direction_t d)
-{
-    p->direction = d;
-    return 0;
-}
-
-static int
 bt_monitor_stats(pcap_t *handle _U_, struct pcap_stat *stats)
 {
     stats->ps_recv = 0;
@@ -200,7 +193,7 @@
     handle->read_op = bt_monitor_read;
     handle->inject_op = bt_monitor_inject;
     handle->setfilter_op = install_bpf_program; /* no kernel filtering */
-    handle->setdirection_op = bt_monitor_setdirection;
+    handle->setdirection_op = NULL; /* Not implemented */
     handle->set_datalink_op = NULL; /* can't change data link type */
     handle->getnonblock_op = pcap_getnonblock_fd;
     handle->setnonblock_op = pcap_setnonblock_fd;