[mrp] Increase MRP backoff time for SED sender

When sender is sleepy, it may take more time until it
receives an acknowledgment from a peer, so MRP backoff time
should be extended by the sleepy active interval.

Signed-off-by: Damian Krolik <[email protected]>

src/messaging/ReliableMessageMgr.cpp

@@ -34,6 +34,7 @@
 #include <messaging/ExchangeMgr.h>
 #include <messaging/Flags.h>
 #include <messaging/ReliableMessageContext.h>
+#include <platform/ConnectivityManager.h>
 
 using namespace chip::System::Clock::Literals;
 
@@ -248,6 +249,18 @@ System::Clock::Timestamp ReliableMessageMgr::GetBackoff(System::Clock::Timestamp
     uint32_t jitter = MRP_BACKOFF_JITTER_BASE + Crypto::GetRandU8();
     mrpBackoffTime  = mrpBackoffTime * jitter / MRP_BACKOFF_JITTER_BASE;
 
+#if CHIP_DEVICE_CONFIG_ENABLE_SED
+    // Implement:
+    //   "A sleepy sender SHOULD increase t to also account for its own sleepy interval
+    //   required to receive the acknowledgment"
+    DeviceLayer::ConnectivityManager::SEDIntervalsConfig sedIntervals;
+
+    if (DeviceLayer::ConnectivityMgr().GetSEDIntervalsConfig(sedIntervals) == CHIP_NO_ERROR)
+    {
+        mrpBackoffTime += System::Clock::Timestamp(sedIntervals.ActiveIntervalMS);
+    }
+#endif
+
     return mrpBackoffTime;
 }