Allow setting a custom grace period for LinuxDVB adapters

When using Astrometa to tune to DVB-T2 muxes in Poland, the scans are reported
as complete but the found services have zero elementary services due to the scan
period being too short in order to fetch PMTs.

This change allows overriding the default grace period of 5 seconds with a
custom value. I successfully scanned all services with this setting changed to
15 for this particular adapter/mux combination.

Author: lighterowl

src/input/mpegts/linuxdvb/linuxdvb_frontend.c

@@ -244,6 +244,18 @@ const idclass_t linuxdvb_frontend_class =
       .opts     = PO_ADVANCED,
       .off      = offsetof(linuxdvb_frontend_t, lfe_old_status),
     },
+    {
+      .type     = PT_U32,
+      .id       = "grace_period",
+      .name     = N_("Scan grace period (seconds)"),
+      .desc     = N_("The maximum amount of time to allow this adapter "
+                     "to complete a scan of a mux. If you're getting "
+                     "failed or incomplete scans (for example, missing "
+                     "services) despite a strong signal, try increasing "
+                     "this value. Ignored for DVB-S."),
+      .opts     = PO_ADVANCED,
+      .off      = offsetof(linuxdvb_frontend_t, lfe_grace_period),
+    },
     {}
   }
 };
@@ -593,10 +605,7 @@ static int
 linuxdvb_frontend_get_grace ( mpegts_input_t *mi, mpegts_mux_t *mm )
 {
   linuxdvb_frontend_t *lfe = (linuxdvb_frontend_t*)mi;
-  int r = 5;
-  if (lfe->lfe_satconf)
-    r = linuxdvb_satconf_get_grace(lfe->lfe_satconf, mm);
-  return r;
+  return lfe->lfe_satconf ? linuxdvb_satconf_get_grace(lfe->lfe_satconf, mm) : lfe->lfe_grace_period;
 }
 
 static int
@@ -2167,6 +2176,7 @@ linuxdvb_frontend_create
   lfe->lfe_pids_use_all = 1;
   lfe->lfe_sig_multiplier = 100;
   lfe->lfe_snr_multiplier = 100;
+  lfe->lfe_grace_period = 5;
   lfe = (linuxdvb_frontend_t*)mpegts_input_create0((mpegts_input_t*)lfe, idc, uuid, conf);
   if (!lfe) return NULL;
 

src/input/mpegts/linuxdvb/linuxdvb_private.h

@@ -150,6 +150,7 @@ struct linuxdvb_frontend
   int                       lfe_lna;
   uint32_t                  lfe_sig_multiplier;
   uint32_t                  lfe_snr_multiplier;
+  uint32_t                  lfe_grace_period;
 
   /*
    * Satconf (DVB-S only)