Dedicated NIC for SQL Server "Always ON"

Hello,

We are trying to setup SQL Server Always ON dedicated NIC.

This is what we have done:

1) We have added the additional NIC on all the nodes partitciapting in "Always ON" and gave that NIC a FQDN. We are using that FQDN in "ENDpoint URL" while going through "Always ON" wizard.

2) We have not changed anthing in "Always On" EndPoint, script of which is listed below:

CREATE ENDPOINT [Hadr_endpoint] STATE=STARTED AS TCP (LISTENER_PORT = 5022, LISTENER_IP = ALL)

FOR DATA_MIRRORING (ROLE = ALL, AUTHENTICATION = WINDOWS NEGOTIATE , ENCRYPTION = REQUIRED ALGORITHM AES)

GO

We tested this by doing bulk insert in one of the database from Availability Group and observed that Secondary Replica is receiving traffic on dedicated NIC but for Primary Replica we saw the tarffic was going through both dedicated and non dedicated NIC. 
How can we ensure that Primary also uses dedicated NIC ? Is it mendatory to setup Listener_IP to the IP of dedicated NIC in the Endpoint ?

Thanks in advance