Remove unnecessary lock of changeState

[BewareMyPower]

Motivation

There's no need to lock the changeState method. We don't need the whole operation is atomic. Instead, we just need that c.setState(state) takes effect so that c.cond.Broadcast() can broadcast the correct notification that the state has been changed successfully. #451 changed state field to an atomic variable, so we don't need the lock for changing state anymore.

I guess the lock for changeState was added when the state field was just a normal int32 variable. But #451 didn't remove the lock.

Modifications

Remove the Lock()/Unlock() calls in changeState, then reuse changeState in connection.Close().

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

[BewareMyPower]

There's a CI failure caused by

go: gopkg.in/[email protected]: git fetch -f origin refs/heads/*:refs/heads/* refs/tags/*:refs/tags/* in /pkg/mod/cache/vcs/7e5fa1eab4705eb80c9746632736cea906708d060702d529df6241d1c8c2c9f9: exit status 128:
	fatal: unable to access 'https://gopkg.in/check.v1/': server certificate verification failed. CAfile: none CRLfile: none
go: error loading module requirements

[freeznet]

LGTM