The current implementation of `MapUpgradeErr` implements `InboundUpgrade`
and `OutboundUpgrade` and applies the transformation in both cases which
means that mapping is always applied to inbound and outbound upgrade
errors. This commit uses separate `MapInboundUpgradeErr` and
`MapOutboundUpgradeErr` types which implements both traits but only map
errors in one direction.
The current implementation of `MapUpgrade` implements `InboundUpgrade`
and `OutboundUpgrade` and applies the transformation in both cases which
means that mapping is always applied to inbound and outbound upgrades.
This commit uses separate `MapInboundUpgrade` and `MapOutboundUpgrade`
types which implements both traits but only map in one direction.
