read/writers are not concurrent in handlers
and self contained - no need to use atomics on
them.
avoids unnecessary contentions where it's not
required.
When reading `TrafficMeter` values, there was a value receiver.
This means that receivers are copied unsafely when invoked.
Fixes race seen with `-race` build.
Traffic metering was not protected against concurrent updates.
```
WARNING: DATA RACE
Read at 0x00c02b0dace8 by goroutine 235:
github.com/minio/minio/cmd.setHTTPStatsHandler.func1()
d:/minio/minio/cmd/generic-handlers.go:360 +0x27d
net/http.HandlerFunc.ServeHTTP()
...
Previous write at 0x00c02b0dace8 by goroutine 994:
github.com/minio/minio/internal/http/stats.(*IncomingTrafficMeter).Read()
d:/minio/minio/internal/http/stats/http-traffic-recorder.go:34 +0xd2
```
This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`
