Go 1.19: use atomic.Pointer instead of atomic.Value

[marten-seemann]

There's a few places in our codebase where we're currently using an atomic.Value:

p2p/net/connmgr/decay.go
41:     lastTick atomic.Value

p2p/net/mock/mock_stream.go
34:     protocol atomic.Value

p2p/host/autonat/autonat.go
36:     status atomic.Value

p2p/net/swarm/swarm_stream.go
27:     protocol atomic.Value

p2p/net/swarm/swarm.go
149:    streamh atomic.Value

Go 1.19 added a atomic.Pointer, which makes use of generics, and allows us to do a type-safe atomic store and load operation. We should replace all uses of atomic.Value with atomic.Pointer.

This can be done as soon as Unified CI is updated and we've dropped support for Go 1.18.

[marten-seemann]

#2073 was just merged, so this is ready to go now. @sukunrt Do you want to give it a shot?

[sukunrt]

sure! I'll pick this.