ONOS-508: Implement IPv6, ICMP6 and NeighborAdvertisement class

Create ICMP6 class, which is mostly like ICMP

Change-Id: I11d7abec4a8f1fd202e5dfb0a500f621773c2c3a

Create IPv6 class, which is mostly like IPv4

Change-Id: I7a301a0f94263df5d6d30f73050332ec7acfe611

Register handler class of IPv6 to Ethernet

Change-Id: Iccdef1680664520f9d66360a289809710982ce54

Fix FIXED_HEADER_LENGTH

Change-Id: Iff4fb22638416595f2865ff46b682a0579ba33d5

Fix payloadLength

Change-Id: I8dea4dd52f0bb5926fbff0d9e74fdd19404cabff

Add unittest for serialize

Change-Id: If194aa2530ce517a33b36b97b8478b0a4c463954

Add unittest for deserialize. Fix assertArrayEquals. Refine test structure.

Change-Id: I94f2a348b2be2f5907d8bac6b9029b37eb31456d

Payload length should be handled during serializing/deserializing procedure

Change-Id: Ib079bf939a01a38356c824ed972793293ed8ca1e

Add unittest for comparator

Change-Id: I937dd9330d7c23a81ecd8434ac0fcf7345cc5c00

Fix typo. Fix checkstyle error

Change-Id: I2fe1af81c65416b0fddaa0fb9ae206b87b889628

Add implementation and unittest for NeighborAdvertisement

Change-Id: I7610462a5712f9fee5be0416c08e1de302e0780d

Register handler class of NeighborAdvertisement to ICMP6

Change-Id: I3a7a9cf044cfdcd8908579942c159c2f0aad198d