From: Dongli Zhang <redacted>
Date: Mon, 31 Oct 2016 13:38:29 +0800

While grant reference is of type uint32_t, xen-netfront erroneously casts
it to signed short in BUG_ON().

This would lead to the xen domU panic during boot-up or migration when it
is attached with lots of paravirtual devices.

Signed-off-by: Dongli Zhang <redacted>

Since this is consistent with how the macros in linux/err.h handle "is
this an error" checks, this change looks good to me.

Applied, thanks.