Oh, I misunderstood. Try something like this:
def __init__(self):
    super(DNet, self).__init__()
    self.conv2_1 = nn.Conv2d(1, 2, 3, 1, 1)
    self.relu_1 = nn.ReLU()
    self.maxpool_1 = nn.MaxPool1d(2, 2)
    self.conv2_2 = nn.Conv2d(2, 3, 1, 1, 4)
    self.relu_2 = nn.ReLU()
    self.maxpool_2 = nn.MaxPool1d(2, 2)
    self.conv2_3 = nn.Conv2d(2, 3, 1, 0, 8)
    self.fc = nn.Linear(8, 1)

    self.apply(self._weight_init)

def _weight_init(self, m):
    if not isinstance(m, nn.ReLU):
        (your init code)