Manager: ignore return value on dev attach
Merge branch 'master' of git://github.com/mirage/mirage-net
switch to encouraging scatter-gather all the time, rather than playing tricks with packet header buffers. This simplifies the output stack and removes the need for the `Frame` module.
(still a WIP)
Install the packed `cmx` along with the `cmxa` to ensure that the compiler can do cross-module optimization (this is not a fatal error, but will impact performance if the `cmx` file is not present).