v2/checksum: use asserts for crash-hard programming errors
v2/checksum: use asserts for crash-hard programming errors

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