libnetwork: protect field access with libnetwork to avoid possible data race

[yanke-xu]

Description

Fixed inconsistency and also potential data race in moby/moby/blob/master/libnetwork/agent.go and moby/moby/blob/master/libnetwork/endpoint.go:
myAliases is read/written many times in moby/moby/blob/master/libnetwork/agent.go and moby/moby/blob/master/libnetwork/endpoint.go;

https://github.com/moby/moby/blob/master/libnetwork/agent.go#L681 is read without a Lock，
https://github.com/moby/moby/blob/master/libnetwork/endpoint.go#L221 is write with a Lock。

A data race may happen when the two operations are called in parallel.

In order to avoid potential data race here, I use xx.RLock(); defer xx.RUnlock() to make sure that all usages of items is in critical section.

Reproduce

Nil

Expected behavior

Data Race

docker version

Nil

docker info

Nil

Additional Info

No response