Prevent double activation of admin interrupt in ENA

The resource is already being activated in the bus_alloc_resource(),
because the flag RF_ACTIVE is being passed.

Double activation on arm64 is causing kernel panic.

Version of the driver was upgraded to 0.8.4.

Submitted by: Michal Krawczyk <mk@semihalf.com>
Reported-by: Greg V <greg@unrelenting.technology>
Tested-by: cperciva, Greg V <greg@unrelenting.technology>
Obtained from: Semihalf
MFC after: 2 weeks
Sponsored by: Amazon, Inc.
Differential revision: https://reviews.freebsd.org/D19655