MINOR: http-rules: Group all processing of early-hint rule in its case clause

MINOR: http-rules: Group all processing of early-hint rule in its case clause

To know if the 103 response start-line must be added, we test if it is the first
rule of the ruleset or if the previous rule is not an early-hint rule. And at
the end, to know if the 103 response must be terminated, we test if it is the
last rule of the ruleset or if the next rule is not an early-hint rule. This
way, all the code dealing with early-hint rules is grouped in its case clause.