rpc: make server send negotiation frame back before closing connection on error
rpc: make server send negotiation frame back before closing connection on error

This will allow client to detect negotiation failure properly.

dreamsxin/seastar,syuu1228/seastar,kjniemi/seastar,sjperkins/seastar,cloudius-systems/seastar,syuu1228/seastar,scylladb/seastar,cloudius-systems/seastar,dreamsxin/seastar,cloudius-systems/seastar,dreamsxin/seastar,sjperkins/seastar,scylladb/seastar,avikivity/seastar,avikivity/seastar,avikivity/seastar,kjniemi/seastar,kjniemi/seastar,syuu1228/seastar,scylladb/seastar,sjperkins/seastar