curl_easy_reset : fix HTTP Retry mechanism

[FreeYourSoul]

I did this

By using the easy interface, I was using the same http connection (and reset it a each use) in order to not waste resources starting connection over and over, working perfectly fine on version 7.70, since version 7.72, it didn't work anymore

The issue

The issue is comming from the retry mechanism that has been re factorized, the retry is now set in the state data of the connection in
conn->state.retrycount.
But the issue is that this new value introduced is not reset to 0 when calling curl_easy_reset, which makes project using this reset feature not working anymore

curl/libcurl version

7.72

I attach the fix directly to this issue

[bagder]

Forgot the attachment?

[FreeYourSoul]

#5975

Sorry, you commented faster than I do the PR.