add debug log for malformed PATH payload

Log path_len and len when the bounds check fails, making it easier to
diagnose malformed or corrupt packets during development.

src/Mesh.cpp

@@ -155,7 +155,10 @@ DispatcherAction Mesh::onRecvPacket(Packet* pkt) {
                 uint8_t path_len = data[k++];
                 uint8_t hash_size = (path_len >> 6) + 1;
                 uint8_t hash_count = path_len & 63;
-                if (k + hash_size*hash_count + 1 > len) break;  // bounds check: need path bytes + extra_type byte
+                if (k + hash_size*hash_count + 1 > len) {  // bounds check: need path bytes + extra_type byte
+                  MESH_DEBUG_PRINTLN("%s Mesh::onRecvPacket(): bad PATH payload format, path_len=%d len=%d", getLogDateTime(), (int)path_len, (int)len);
+                  break;
+                }
                 uint8_t* path = &data[k]; k += hash_size*hash_count;
                 uint8_t extra_type = data[k++] & 0x0F;   // upper 4 bits reserved for future use
                 uint8_t* extra = &data[k];