Adjust unit tests to account for fix to bug 22753.

Our mock network put all the guards on the same IPv4 address, which
doesn't fly when we start applying EnforceDistinctSubnets.  So in
this commit, I disable EnforceDistinctSubnets when running the old
guard_restriction_t test.

This commit also adds a regression test for #22753.

src/test/test_entrynodes.c

@@ -121,6 +121,8 @@ big_fake_network_setup(const struct testcase_t *testcase)
 
     n->is_running = n->is_valid = n->is_fast = n->is_stable = 1;
 
+    /* Note: all these guards have the same address, so you'll need to
+     * disable EnforceDistinctSubnets when a restriction is applied. */
     n->rs->addr = 0x04020202;
     n->rs->or_port = 1234;
     n->rs->is_v2_dir = 1;
@@ -1846,14 +1848,17 @@ test_entry_guard_select_for_circuit_confirmed(void *arg)
   tt_uint_op(state, OP_EQ, GUARD_CIRC_STATE_USABLE_IF_NO_BETTER_GUARD);
   tt_i64_op(g2->last_tried_to_connect, OP_EQ, approx_time());
 
-  // If we say that the next confirmed guard in order is excluded, we get
-  // The one AFTER that.
+  // If we say that the next confirmed guard in order is excluded, and
+  // we disable EnforceDistinctSubnets, we get the guard AFTER the
+  // one we excluded.
+  get_options_mutable()->EnforceDistinctSubnets = 0;
   g = smartlist_get(gs->confirmed_entry_guards,
                      smartlist_len(gs->primary_entry_guards)+2);
   entry_guard_restriction_t rst;
   memset(&rst, 0, sizeof(rst));
   memcpy(rst.exclude_id, g->identity, DIGEST_LEN);
   g2 = select_entry_guard_for_circuit(gs, GUARD_USAGE_TRAFFIC, &rst, &state);
+  tt_ptr_op(g2, OP_NE, NULL);
   tt_ptr_op(g2, OP_NE, g);
   tt_int_op(g2->confirmed_idx, OP_EQ,
             smartlist_len(gs->primary_entry_guards)+3);
@@ -1873,6 +1878,16 @@ test_entry_guard_select_for_circuit_confirmed(void *arg)
   tt_assert(g->is_pending);
   tt_int_op(g->confirmed_idx, OP_EQ, -1);
 
+  // If we EnforceDistinctSubnets and apply a restriction, we get
+  // nothing, since we put all of the nodes in the same /16.
+  // Regression test for bug 22753/TROVE-2017-006.
+  get_options_mutable()->EnforceDistinctSubnets = 1;
+  g = smartlist_get(gs->confirmed_entry_guards, 0);
+  memset(&rst, 0, sizeof(rst));
+  memcpy(rst.exclude_id, g->identity, DIGEST_LEN);
+  g2 = select_entry_guard_for_circuit(gs, GUARD_USAGE_TRAFFIC, &rst, &state);
+  tt_ptr_op(g2, OP_EQ, NULL);
+
  done:
   guard_selection_free(gs);
 }