mod_http2: merge r1726798 from trunk.

Fix warnings:
modules/http2/h2_util.c|174| warning: suggest parentheses around ‘+’ in operand of ‘&’
modules/http2/h2_util.c|176| warning: suggest parentheses around ‘+’ in operand of ‘&’

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1726801 13f79535-47bb-0310-9956-ffa450edef68