Use tx_disable_channel with media_lanes_mask

[rajann]

Description

Invoke tx_disable_channel() api using the correct media_lanes_mask in case of subport shut/no shut operations

 (i.e) existing tx_disable_channel( ) api is being used with host_lanes_mask as of now.  
        This is not aligning with the subport concept where media_lane start wont match with host_lanes start.

As part of the fix, introduced an api to retrieve media_lanes_mask and use it as part of the tx_disable_channel() api

How Has This Been Tested?

Using 4x100G and 2x100G breakout modules

• create 4 and 2 subports on 4x100G and 2x100G modules respectively.
• Check whether all the subports are operationally up
• Verify the upper page 10 for outputdisable values and page 11 for the data path state
• Shut each subports one at a time and verify the operational status of every subports in this module
• Unshut each subport one at a time and verify the operational status of every subports in this module
• At each step verify the values in page10h and page 11h
• Verified the subports with traffic

[mihirpat1]

Can you please help in resolving the test case failure seen with this changeset?

[rajann]

Yes fixed the indentation issue and committed