Actually expire next hops when deleting a VLAN

[gizmoguy]

Fixes bug introduced in #4850, ofmsgs returned by expire_vlan_nexthops() were not merged with ofmsgs from del_vlan() and returned.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.74%. Comparing base (2275552) to head (8944e4c).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4863   +/-   ##
=======================================
  Coverage   91.74%   91.74%           
=======================================
  Files          46       46           
  Lines        9084     9084           
=======================================
  Hits         8334     8334           
  Misses        750      750           

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