title: 'max_length' is ignored when used with IntegerField
body: <p>I have this model</p>
  <pre><code>class MyUser(AbstractBaseUser):
      ##username =models.U
      email=models.EmailField(
          verbose_name='email address',
          max_length=255,
          unique=True,
      )
      date_of_birth=models.DateField()
      picture =models.ImageField(upload_to='images/users',null=True,verbose_name=&quot;&quot;)
      is_active =models.BooleanField(default=True)
      phone_number = models.IntegerField(max_length=12,unique=True,null=False,verbose_name='phone')
      is_admin = models.BooleanField(default=False)
      #credits =models.PositiveIntegerField(default=100)
      linkedin_token=models.TextField(blank=True ,default='')
      expiry_date=models.DateTimeField(null=True, blank=True)
      objects=UserManger()
  </code></pre>
  <p>when i run <code>python manage.py makemigrations </code> I got this error</p>
  <blockquote>
  <p>WARNINGS:
  Accounts.MyUser.phone_number: (fields.W122) 'max_length' is ignored when used with IntegerField.
  HINT: Remove 'max_length' from field
  It is impossible to add a non-nullable field 'phone_number' to myuser without specifying a default. This is because the database needs something to populate existing rows.</p>
  </blockquote>
  <p>can any one help me ?</p>