wsdd2: fix infinite loop when BI_PARM is never set

If BI_PARM is never set, it's "" and causes
infinite loop (before my PR sent upstream) or
error out (after my PR sent upstream).
Append -b option only if it's valid.

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

net/wsdd2/files/wsdd2.init

@@ -68,7 +68,7 @@ start_service() {
 	[ -n "$ifname" ] && procd_append_param command -i "$ifname"
 	procd_append_param command -N "$NB_PARM"
 	procd_append_param command -G "$WG_PARM"
-	procd_append_param command -b "$BI_PARM"
+	[ "x${BI_PARM}" != "x" ] && procd_append_param command -b "$BI_PARM"
 	procd_set_param respawn
 	procd_set_param file "$SMB_CONF"
 	procd_close_instance