netfront: remove XN_LOCK_{INIT,DESTROY}

[liuw_liuw.name]

Summary

Multiqueue feature will make the number of queues dynamic, so XN_LOCK_INIT won't be that useful. Remove the macro and call mtx_init directly.

XN_LOCK_DESTROY is just dead code.

[royger]

LGTM, only a minor comment that I can fix while committing.

sys/dev/xen/netfront/netfront.c

1877

The lock names should be shorter so they can be properly displayed when using top, I would rename "_xennet_tx" to "xntx" and the same for the others ("xnrx", "xnsc").

And "network transmit lock" -> "netfront transmit lock".

[liuw_liuw.name]

sys/dev/xen/netfront/netfront.c

1877

Didn't bother to change existing long names when I wrote the patch, but of course the changes you suggested are fine by me.