Fixes two deprecation warnings

`this._healthCheck()`& `this._handle` caused deprecation warnings.

Author: n-thumann

lib/dgram.js

@@ -835,7 +835,7 @@ Socket.prototype.dropMembership = function(multicastAddress,
 Socket.prototype.addSourceSpecificMembership = function(sourceAddress,
                                                         groupAddress,
                                                         interfaceAddress) {
-  this._healthCheck();
+  healthCheck(this);
 
   if (typeof sourceAddress !== 'string') {
     throw new errors.TypeError('ERR_INVALID_ARG_TYPE', 'sourceAddress',
@@ -847,7 +847,7 @@ Socket.prototype.addSourceSpecificMembership = function(sourceAddress,
                                'string');
   }
 
-  const err = this._handle.addSourceSpecificMembership(sourceAddress,
+  const err = this[kStateSymbol].handle.addSourceSpecificMembership(sourceAddress,
                                                        groupAddress,
                                                        interfaceAddress);
   if (err) {
@@ -859,7 +859,7 @@ Socket.prototype.addSourceSpecificMembership = function(sourceAddress,
 Socket.prototype.dropSourceSpecificMembership = function(sourceAddress,
                                                          groupAddress,
                                                          interfaceAddress) {
-  this._healthCheck();
+  healthCheck(this);
 
   if (typeof sourceAddress !== 'string') {
     throw new errors.TypeError('ERR_INVALID_ARG_TYPE', 'sourceAddress',
@@ -871,7 +871,7 @@ Socket.prototype.dropSourceSpecificMembership = function(sourceAddress,
                                'string');
   }
 
-  const err = this._handle.dropSourceSpecificMembership(sourceAddress,
+  const err = this[kStateSymbol].handle.dropSourceSpecificMembership(sourceAddress,
                                                         groupAddress,
                                                         interfaceAddress);
   if (err) {