mon: fix forwarded request features when requests are resent

Pass the features in explicitly so that we can use messages we've just
decoded in resend_routed_requests().

Keep the features in struct RoutedRequest.

Renamed conn_features -> con_features while we are here.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #990 from ceph/wip-fix-mon-fwd

mon: fix forwarded request features when requests are resent

Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>