Fix Publicize Share Connection Toggle

[gititon]

When you first connect a social account via Publicize, you are presented with an option to share the connection among all authors. This will give all authors the ability to share their posts via this social media connection. Unfortunately, even when you enable this option, the setting doesn't save on WPCOM.

Fixes #10930

Changes proposed in this Pull Request:

This PR ensures the correct Publicize Connection id is sent in the request to enable all authors to share the connection.

Testing instructions:

Spin up a JN site with the branch, here
Go to /wp-admin/options-general.php?page=sharing
Click the button to connect any service.
Go through the flow in the popup.
After connecting, enable the setting to make the connection global.
Close the popup
Open https://wordpress.com/sharing/your-domain
Expand the connection.
Ensure that it's set as shared/global.

Proposed changelog entry for your changes:

No changelog entry needed

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: January 10, 2019.
Scheduled code freeze: January 3, 2019

Generated by 🚫 dangerJS against bbf9f3a

[lezama]

Good catch! I wonder how long has this been around

[mdawaffe]

Looks like I introduced the bug in 5d8f264.

[tyxla]

Thanks for fixing this 👐