iwlwifi: mvm: loosen nssn comparison to reorder buffer head

iwlwifi: mvm: loosen nssn comparison to reorder buffer head

Up till now, the reorder buffer uses standard spec based comparison
when comparing the buffer status to NSSN. This indeed works for the
regular case, since we shouldn't cross the 2048 boundary without
getting a frame release notification.
However, this is problematic due to packet filtering that may be
performed by the FW while we are in d0i3. Theoretically we may
filter over 2048 packets, and then the check of the NSSN will get
incorrect.
Change the comparison to always trust nssn unless it is 64 or less
frames behind the head - which might happen due to a timeout.
This new comparison is to be used only when comparing reorder buffer
head with nssn, and not when comparing the packet SN to nssn or
reorder buffer head.
Put this in a separate commit as the logic is a bit tricky and
stands for its own commit message.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>