[FAB-2756] Batch gossip state transfer request

Currently newly joined peer while syncing with rest of the network able
to send request to retrive entire ledger in one message, which is
in-efficient and presents potential exposure for denial of service
attacks.

This commits refactor gossip state trafer message in a way it
requires only to send two numbers representing the interval of required
missing blocks and makes sure this interval could not be longer than
specified by algorithm value.

Change-Id: I12cbf1922c39032125e1d168cea57eafa1013a32
Signed-off-by: Artem Barger <bartem@il.ibm.com>

gossip/comm/mock/mock_comm_test.go

@@ -46,7 +46,8 @@ func TestMockComm(t *testing.T) {
 
 	comm2.Send((&proto.GossipMessage{
 		Content: &proto.GossipMessage_StateRequest{&proto.RemoteStateRequest{
-			SeqNums: []uint64{1, 2, 3},
+			StartSeqNum: 1,
+			EndSeqNum:   3,
 		}},
 	}).NoopSign(), &comm.RemotePeer{"first", common.PKIidType("first")})