gall: clear outstanding ack queue on-load

This will fix the issue described in #2867 for ducts that have already
triggered the bug.  This will also send spurious acks for any messages
that are outstanding at the time of the upgrade, but I don't believe
this will cause a serious problem.

bin/solid.pill

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:ecfe53c9e00d8cba244c85eb0ec0ed3b4e8ac07737bb0c6a7aa57d6c52f52c85
-size 15993675
+oid sha256:8da3208fcb4424da285159aa3d923bba941ad25a026b30ab0e58e54f4ecac80b
+size 12885759

pkg/arvo/sys/vane/gall.hoon

@@ -55,7 +55,7 @@
 ++  state
   $:  :: state version
       ::
-      %4
+      %5
       :: agents by ship
       ::
       =agents
@@ -1685,16 +1685,32 @@
   =?  all-state  ?=(%3 -.all-state)
     (state-3-to-4 all-state)
   ::
-  ?>  ?=(%4 -.all-state)
+  =?  all-state  ?=(%4 -.all-state)
+    (state-4-to-5 all-state)
+  ::
+  ?>  ?=(%5 -.all-state)
   gall-payload(state all-state)
   ::
   ::  +all-state: upgrade path
   ::
-  ++  all-state  $%(state-0 state-1 state-2 state-3 ^state)
+  ++  all-state  $%(state-0 state-1 state-2 state-3 state-4 ^state)
+  ::
+  ++  state-4-to-5
+    |=  =state-4
+    ^-  ^state
+    %=    state-4
+        -  %5
+        outstanding.agents  ~
+    ==
+  ::
+  ++  state-4
+    $:  %4
+        =agents
+    ==
   ::
   ++  state-3-to-4
     |=  =state-3
-    ^-  ^state
+    ^-  state-4
     %=    state-3
         -  %4
         outstanding.agents  ~