beacon-chain/rpc/service.logNewClientConnection has unsafe map access

[prestonvanloon]

User reported concurrent map access panic and their logs point to these lines of code.

prysm/beacon-chain/rpc/service.go

Lines 403 to 408 in 78465e2

	if !s.connectedRPCClients[clientInfo.Addr] {
	log.WithFields(logrus.Fields{
	"addr": clientInfo.Addr.String(),
	}).Infof("New gRPC client connected to beacon node")
	s.connectedRPCClients[clientInfo.Addr] = true
	}

See comments here: #5576 (comment)

Assigning to @rauljordan as the original author of this log in #6233.

cc: @stefa2k

[stefa2k]

looking good, service has been stable for 16h now without this errors