Ensure vars used atomically in peer are aligned.

The sync.atomic requires alignment of variables used atomically on ARM.
This commit moves the connected and disconnect variables in the peer
struct up so they are aligned.

Fixes #157.

peer.go

@@ -144,12 +144,12 @@ type peer struct {
 	server             *server
 	btcnet             btcwire.BitcoinNet
 	started            int32
+	connected          int32
+	disconnect         int32 // only to be used atomically
 	conn               net.Conn
 	addr               string
 	na                 *btcwire.NetAddress
 	inbound            bool
-	connected          int32
-	disconnect         int32 // only to be used atomically
 	persistent         bool
 	knownAddresses     map[string]struct{}
 	knownInventory     *MruInventoryMap