Implement some of the missing IPv6 flowmod treatments

Work toward ONOS-509

The following treatments are added/implemented:
  - IPV6_SRC
  - IPV6_DST
  - IPV6_FLABEL

Also:
 - Renamed L3ModificationInstruction.L3SubType.IP_SRC and IP_DST
   to IPV4_SRC and IPV4_DST (for naming consistency).
 - Few minor fixes in related code: Javadocs, comments, log messages,
   and IP address usage.

Change-Id: I551056f767a37e7cb6ae7d79f4a3929183500b57
diff --git a/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java b/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java
index 91edcbf..98cb3b2 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java
@@ -120,7 +120,7 @@
         public Builder setIpDst(IpAddress addr);
 
         /**
-         * Decrease the TTL in IP header by one.
+         * Decrement the TTL in IP header by one.
          *
          * @return a treatment builder
          */