iwlwifi: add {ack, plpc}_check module parameters

iwlwifi: add {ack, plpc}_check module parameters

BugLink: http://bugs.launchpad.net/bugs/788691

commit b7977ffaab5187ad75edaf04ac854615cea93828 upstream.

Add module ack_check, and plcp_check parameters. Ack_check is disabled
by default since is proved that check ack health can cause troubles.
Plcp_check is enabled by default.

This prevent connection hangs with "low ack count detected" messages.

Resolves:
https://bugzilla.redhat.com/show_bug.cgi?id=666646

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Steve Conklin <sconklin@canonical.com>