Small extensions in server driver

First extension is the ability to prevent the installation
of a full wildcard rule, when only one rule is present per
NIC. Such a rule will redirect all the system's load on one
core, which is undesirable.
Second, we introduce the ability to detect the duration of
load on a core by converting the boolean field isBusy to
a timestamp busySince.

Addressed code review suggestions.

Change-Id: I631cf322ee3724d9f1f97246d4189b5b2a008a76
Signed-off-by: Georgios Katsikas <katsikas.gp@gmail.com>
diff --git a/drivers/server/src/main/java/org/onosproject/drivers/server/devices/nic/NicFlowRule.java b/drivers/server/src/main/java/org/onosproject/drivers/server/devices/nic/NicFlowRule.java
index 1215b6f..9083395 100644
--- a/drivers/server/src/main/java/org/onosproject/drivers/server/devices/nic/NicFlowRule.java
+++ b/drivers/server/src/main/java/org/onosproject/drivers/server/devices/nic/NicFlowRule.java
@@ -206,6 +206,13 @@
     boolean hasTransport();
 
     /**
+     * Returns whether this rule is a full wildcard or not.
+     *
+     * @return boolean full wildcard status
+     */
+    boolean isFullWildcard();
+
+    /**
      * Returns the set of actions of this rule.
      *
      * @return rule's set of actions