[4206b] Fixed two typos in the Pkt4 and Pkt6 methods.

src/lib/dhcp/pkt4.cc

@@ -362,7 +362,7 @@ Pkt4::getLabel() const {
     } catch (...) {
         // This should not happen with the current code, but we may add extra
         // sanity checks in the future that would possibly throw if
-        // the hwaddr lenght is 0.
+        // the hwaddr length is 0.
         label << " (malformed hw address)";
     }
 

src/lib/dhcp/pkt6.cc

@@ -566,7 +566,7 @@ Pkt6::getClientId() const {
         // process of logging something for this packet. So the only
         // choice left is to return an empty pointer.
     }
-    return DuidPtr();
+    return (DuidPtr());
 }
 
 isc::dhcp::OptionCollection