MB-47457: [BP] NetworkType:default for gocbcore Agent/DCPAgent configs

+ This will essentially force agents belonging to FTS to always
  use the internal IP for communication with KV and cluster manager.

(Reviewed-on: http://review.couchbase.org/c/cbgt/+/157795)

Change-Id: If0dc93f92d401a8e9f5b5707cd10ed2fd358c141
Reviewed-on: http://review.couchbase.org/c/cbgt/+/159057
Well-Formed: Restriction Checker
Reviewed-by: Sreekanth Sivasankaran <sreekanth.sivasankaran@couchbase.com>
Tested-by: Abhinav Dangeti <abhinav@couchbase.com>

feed_dcp_gocbcore.go

@@ -331,6 +331,7 @@ func setupDCPAgentConfig(
 		Auth:             auth,
 		ConnectTimeout:   GocbcoreConnectTimeout,
 		KVConnectTimeout: GocbcoreKVConnectTimeout,
+		NetworkType:      "default",
 		UseCollections:   true,
 		UseOSOBackfill:   useOSOBackfill,
 		UseStreamID:      useStreamID,

gocbcore_utils.go

@@ -52,6 +52,7 @@ func setupAgentConfig(name, bucketName string,
 		Auth:             auth,
 		ConnectTimeout:   GocbcoreConnectTimeout,
 		KVConnectTimeout: GocbcoreKVConnectTimeout,
+		NetworkType:      "default",
 		UseCollections:   true,
 	}
 }