Merge pull request #2617 in SNORT/snort3 from ~SHRARANG/snort3:appid_http_fixes to...

Merge pull request #2617 in SNORT/snort3 from ~SHRARANG/snort3:appid_http_fixes to master

Squashed commit of the following:

commit b7ab85456eef818f937b46a2451a2de19c1961cc
Author: Shravan Rangaraju <shrarang@cisco.com>
Date:   Fri Nov 13 16:35:59 2020 -0500

    appid: do not override http fields with empty values

commit adcccb07de640c0298b5cf4c89da19fe36d6a436
Author: Shravan Rangaraju <shrarang@cisco.com>
Date:   Fri Nov 13 16:35:29 2020 -0500

    appid: for http2 flow, return service id as http2 when no streams are yet created