map: fix hop limit expiration at br

Before this patch, packet was dropped in ip4-input,
but ip4-map-t node dropped response due to
'security check failed'
This patch checkes if hop_limit==1 and sets error
and next frame and sends icmp6 response correctly

Type: fix

Signed-off-by: Vladimir Ratnikov <vratnikov@netgate.com>
Change-Id: I85a6af58205b05754ef8c45a94817bb84f915c85