v2/handler: initialize inc req/res checksum to known empty w/ type
v2/handler: initialize inc req/res checksum to known empty w/ type

sasa233/tchannel,sasa233/tchannel,Zirpon/tchannel,vanloswang/tchannel,chenwenbin928/tchannel,savaki/tchannel,bunnyblue/tchannel,chenwenbin928/tchannel,i/tchannel,hustxiaoc/tchannel,vanloswang/tchannel,Zirpon/tchannel,chenwenbin928/tchannel,benfleis/tchannel,hustxiaoc/tchannel,vanloswang/tchannel,RyanTech/tchannel,sasa233/tchannel,bunnyblue/tchannel,bunnyblue/tchannel,hustxiaoc/tchannel,Zirpon/tchannel,savaki/tchannel,RyanTech/tchannel,i/tchannel,benfleis/tchannel,savaki/tchannel,benfleis/tchannel,RyanTech/tchannel,i/tchannel