ice: synchronize the misc IRQ when tearing down Tx tracker

commit f0ae1240 upstream.

Since commit 1229b339

 ("ice: Add low latency Tx timestamp read") the
ice driver has used a threaded IRQ for handling Tx timestamps. This change
did not add a call to synchronize_irq during ice_ptp_release_tx_tracker.
Thus it is possible that an interrupt could occur just as the tracker is
being removed. This could lead to a use-after-free of the Tx tracker
structure data.

Fix this by calling sychronize_irq in ice_ptp_release_tx_tracker after
we've cleared the init flag. In addition, make sure that we re-check the
init flag at the end of ice_ptp_tx_tstamp before we exit ensuring that we
will stop polling for new timestamps once the tracker de-initialization has
begun.

Refactor the ts_handled variable into "more_timestamps" so that we can
simply directly assign this boolean instead of relying on an initialized
value of true. This makes the new combined check easier to read.

With this change, the ice_ptp_release_tx_tracker function will now wait for
the threaded interrupt to complete if it was executing while the init flag
was cleared.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Liwei Song <liwei.song@windriver.com>