access: fix VLAN database idempotency

Do not try and match the global VLAN list as printed by the switch.
Instead, only try to realize the truth: there may be some VLANs added
and some removed.

We keep the compact_numlist filter and use it instead of the built-in
vlan_parser when listing VLANs for tagged ports. This is because some
switches compact 1,2,4,5,6 as 1-2,4-6 and others as 1,2,4-6 (see next
commit).

All of this should reduce the number of cases where Ansible reports a
change in configuration where there was in fact no change.

filter_plugins/netbox.py

@@ -14,36 +14,30 @@ class FilterModule(object):
             'iface_vlans': self.iface_vlans
         }
 
-    def compact_numlist(self, nums, sort=True, delimiter=',', range_delimiter='-', max_per_line=None):
+    def compact_numlist(self, nums, sort=True, delimiter=',', range_delimiter='-', min_join=2):
         '''Transform [1,2,3,5,7,8,9] into "1-3,5,7-9".
 
-        If max_per_line is given, return a list of such strings where each string contains at most max_per_line+1 numbers.
-        This emulates how VLAN ranges are displayed by FS switches so we can make ansible check mode work correctly.
+        Do not create a range from fewer than min_join consecutive numbers.
         '''
         if sort:
             nums = sorted(nums)
-        i = 0
-        lines = []
-        line = []
-        nums_in_line = 0
-        while i < len(nums):
-            j = i + 1
-            while j < len(nums) and nums[j]-nums[i] == j-i:
-                j += 1
-            if j > i+1:
-                line += [f'{nums[i]}{range_delimiter}{nums[j-1]}']
-                nums_in_line += 2
+        ranges = []
+        r = []
+        for num in nums:
+            if r and num > r[-1]+1:
+                ranges += [r]
+                r = []
+            r += [num]
+        if r:
+            ranges += [r]
+
+        def format_range(r):
+            if len(r) < min_join:
+                return delimiter.join(str(n) for n in r)
             else:
-                line += [f'{nums[i]}']
-                nums_in_line += 1
-            if max_per_line and nums_in_line >= max_per_line:
-                lines += [delimiter.join(line)]
-                line = []
-                nums_in_line = 0
-            i = j
-        if line:
-            lines += [delimiter.join(line)]
-        return lines if max_per_line else lines[0]
+                return f'{r[0]}{range_delimiter}{r[-1]}'
+
+        return delimiter.join(format_range(r) for r in ranges)
 
     def device_address(self, device):
         '''Return loopback IP addresses for an L3 attached device'''