fix: ensure updateMetaDataMs is 64-bit aligned (#2356)
fix: ensure updateMetaDataMs is 64-bit aligned (#2356)

As per golang/go#41970 any 64-bit variable that is accessed atomically
must be 64-bit aligned and this can be ensured by making it the first
entry in the struct.

Fixes #2337
Shopify/sarama,Shopify/sarama