[MTM-31190][fix]mbbase.cc: Add comments after review

src/modbus/mbbase.cc

@@ -114,12 +114,16 @@ void ModbusModel::addAddress(uint8_t type, uint16_t addr)
         return;
     }
 
+    // Make a pair (start addr, end addr) to queue
     for(auto itr = pm->begin(); itr != pm->end(); ++itr) {
         if (itr->first <= addr && addr <= itr->second){
+            // addr is within the pair's address range
             return;
         } else if (itr->second + 1 == itr->first + limit) {
+            // The pair's address range is already limit
             continue;
         } else if (itr->second + 2 == itr->first + limit) {
+            // The pair's address range will be limit after extension
             if (addr + 1 == itr->first) {
                 itr->first = addr;
                 return;
@@ -130,6 +134,7 @@ void ModbusModel::addAddress(uint8_t type, uint16_t addr)
         } else if (addr + 1 == itr->first) {
             itr->first = addr;
             for(auto i = pm->begin(); i != pm->end(); ++i) {
+                // Extend the pair's address range with another consecutive pair
                 if (addr == i->second + 1) {
                     itr->first = i->first;
                     pm->erase(i);