CVE-2024-42107 ice: Don't process extts if PTP is disabled

In the Linux kernel, the following vulnerability has been resolved:

ice: Don’t process extts if PTP is disabled

The ice_ptp_extts_event() function can race with ice_ptp_release() and
result in a NULL pointer dereference which leads to a kernel panic.

Panic occurs because the ice_ptp_extts_event() function calls
ptp_clock_event() with a NULL pointer. The ice driver has already
released the PTP clock by the time the interrupt for the next external
timestamp event occurs.

To fix this, modify the ice_ptp_extts_event() function to check the
PTP state and bail early if PTP is not ready.