X-pingback header should be generated the same as rel="pingback" link

[mark-k]

Right now the generation of the url for X-pingback is done by a call to get_bloginfo API while the generation of the rel="pingback" link is done by calling bloginf API.
The difference between the two is that the later can be filtered which means that in theory the X-pingback URL will be different than the one in rel="pingback link.

I suggest using the bloginfo API for both as I don't see any reason not to be able to filter the url (right now it points to the XMLRPC end point but people might want to use a different one for pingback to have a distinction in treatment between remote management and commenting)

[dshanske]

I can see good reasons to allow this to be filtered uniformly. One being the possibility of delegating pingback processing to a service function outside of WordPress itself.

[jorbin]

In 38671:

Pings/Trackbacks: Add filter argument to fetching of pingbacks_url in X-pingback header

It is possible to delegate pingback processing to a service function outside of WordPress itself. All other calls in default themes (and likely other themes) uses bloginfo which automatically adds the filter argument of "display". This adds consistency.

Props dshanske.
Fixes #34633.