[4500] Addressed comments

src/bin/dhcp6/dhcp6_hooks.dox

@@ -191,7 +191,7 @@ packet processing. Hook points that are not specific to packet processing
    If a client sends more than one IA_NA option, callouts will be called
    separately for each IA_NA instance. The callout will be called only
    when the update is valid, i.e. conditions such as an invalid addresses
-   or invalid iaid rebindal attempts will not trigger this hook point.
+   or invalid iaid rebinding attempts will not trigger this hook point.
 
  - <b>Next step status</b>: If any callout installed on "lease6_rebind"
    sets the status to SKIP, the server will not rebind the lease. Under these

src/bin/dhcp6/tests/hooks_unittest.cc

@@ -411,6 +411,7 @@ public:
         callout_handle.getArgument("ia_na", callback_ia_na_);
 
         // Let's override some values in the lease
+        ASSERT_TRUE(callback_lease6_);
         callback_lease6_->iaid_          = override_iaid_;
         callback_lease6_->t1_            = override_t1_;
         callback_lease6_->t2_            = override_t2_;
@@ -418,6 +419,7 @@ public:
         callback_lease6_->valid_lft_     = override_valid_;
 
         // Override the values to be sent to the client as well
+        ASSERT_TRUE(callback_ia_na_);
         callback_ia_na_->setIAID(override_iaid_);
         callback_ia_na_->setT1(override_t1_);
         callback_ia_na_->setT2(override_t2_);
@@ -466,6 +468,7 @@ public:
         callout_handle.getArgument("ia_na", callback_ia_na_);
 
         // Let's override some values in the lease
+        ASSERT_TRUE(callback_lease6_);
         callback_lease6_->iaid_          = override_iaid_;
         callback_lease6_->t1_            = override_t1_;
         callback_lease6_->t2_            = override_t2_;
@@ -473,6 +476,7 @@ public:
         callback_lease6_->valid_lft_     = override_valid_;
 
         // Override the values to be sent to the client as well
+        ASSERT_TRUE(callback_ia_na_);
         callback_ia_na_->setIAID(override_iaid_);
         callback_ia_na_->setT1(override_t1_);
         callback_ia_na_->setT2(override_t2_);