Check if leftmost AS matches *remote_as*.

def has_matching_leftmost(self, remote_as):
        """Check if leftmost AS matches *remote_as*."""
        if not self.value or not remote_as:
            return False

        leftmost_seg = self.path_seg_list[0]
        if leftmost_seg and leftmost_seg[0] == remote_as:
            return True

        return False