base-manager: new '--test-low-power-suspend-resume' option

Will request to put the modems in low power mode upon system suspend.

Based on an earlier approach from Jack Song and Nero Zhang, see
https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/1050

src/mm-context.c

@@ -238,6 +238,7 @@ static gboolean  test_no_udev;
 #if defined WITH_SUSPEND_RESUME
 static gboolean  test_no_suspend_resume;
 static gboolean  test_quick_suspend_resume;
+static gboolean  test_low_power_suspend_resume;
 #endif
 #if defined WITH_QRTR
 static gboolean  test_no_qrtr;
@@ -285,6 +286,11 @@ static const GOptionEntry test_entries[] = {
         "Enable quick suspend/resume support for modems which stay on during host suspension",
         NULL
     },
+    {
+        "test-low-power-suspend-resume", 0, 0, G_OPTION_ARG_NONE, &test_low_power_suspend_resume,
+        "Enable support to put the modem in low power mode during suspend/resume",
+        NULL
+    },
 #endif
 #if defined WITH_QRTR
     {
@@ -358,11 +364,18 @@ mm_context_get_test_no_suspend_resume (void)
 {
     return test_no_suspend_resume;
 }
+
 gboolean
 mm_context_get_test_quick_suspend_resume (void)
 {
     return test_quick_suspend_resume;
 }
+
+gboolean
+mm_context_get_test_low_power_suspend_resume (void)
+{
+    return test_low_power_suspend_resume;
+}
 #endif
 
 #if defined WITH_QRTR