Don't allocate a new buffer pool per connection.

[Stebalien]

It looks like we were doing this in secio.

Secio PR: libp2p/go-libp2p-secio#21

Related, pull through the updated go-msgio/mpool. It no longer uses a global lock...

[Stebalien]

On further inspection, it we may have been sharing some buffer pools in some cases as some packages copied the buffer pools while others referenced them (which would have initialized the inner buffer pools). Regardless, this behavior was buggy as hell, prone to deadlocks (copying initialized locks...), and inefficient.

[Kubuxu]

I think this should be fixed by changing https://github.com/libp2p/go-msgio/blob/master/mpool/pool.go#L29 to be a pointer to a Pool.

This way simple re-referencing would not copy the locks.

[Stebalien]

This is actually fixed in master, I just stopped copying around the pool. However, yes, storing this as a reference would probably be a good idea and would prevent things like this from coming up in the future.