filter: 'strict' is the new default

The 'strict' filter policy is less invasive, as it will not touch TTYs
unless there are clear indications that it may be a modem. Under this
mode, the ModemManager-provided blacklist database is not used.

src/mm-context.c

@@ -38,7 +38,7 @@
 static gboolean      help_flag;
 static gboolean      version_flag;
 static gboolean      debug;
-static MMFilterRule  filter_policy = MM_FILTER_POLICY_LEGACY;
+static MMFilterRule  filter_policy = MM_FILTER_POLICY_STRICT;
 static gboolean      no_auto_scan = NO_AUTO_SCAN_DEFAULT;
 static const gchar  *initial_kernel_events;