Setup default wpa_supplicant flags so that it:

* Writes diagnostics to syslog
  * Enables interface matching to hotplug wireless interfaces
  * Uses /etc/wpa_supplicant.conf

etc/defaults/rc.conf

@@ -1,4 +1,4 @@
-#	$NetBSD: rc.conf,v 1.146 2018/10/19 14:11:12 martin Exp $
+#	$NetBSD: rc.conf,v 1.147 2019/01/12 17:38:36 roy Exp $
 #
 # /etc/defaults/rc.conf --
 #	default configuration of /etc/rc.conf
@@ -317,7 +317,7 @@ iscsid=NO
 
 # WPA daemons.
 hostapd=NO		hostapd_flags="-B /etc/hostapd.conf"
-wpa_supplicant=NO	wpa_supplicant_flags="" # -i<if> -c<file>
+wpa_supplicant=NO	wpa_supplicant_flags="-Ms -c /etc/wpa_supplicant.conf"
 
 # Bluetooth configuration
 bluetooth=NO