p2p: fix unsynchronized map access during Server shutdown
p2p: fix unsynchronized map access during Server shutdown

removePeer can be called even after listenLoop and dialLoop have returned.

maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum