ixl(4): Add more debug information for queues' config

Include information about interrupt linked lists in
queue_interrupt_table sysctl and add new debug sysctl queue_int_ctln
allowing to check current interrupt state.

Signed-off-by: Krzysztof Galazka <krzysztof.galazka@intel.com>
Signed-off-by: Eric Joyner <erj@FreeBSD.org>

Reviewed by: erj@
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D45403