ice: prevent tstamp ring allocation for non-PF VSI types

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

ice: prevent tstamp ring allocation for non-PF VSI types

The pf->txtime_txqs bitmap tracks which Tx queues have ETF (Earliest
TxTime First) offload enabled. This bitmap is indexed by queue number
and is set by ice_offload_txtime(), which only operates on PF VSI
queues.

However, ice_is_txtime_ena() does not check the VSI type before
consulting the bitmap. When ETF offload is enabled on PF Tx queue 0,
bit 0 is set in pf->txtime_txqs. During a subsequent PCI reset
rebuild, the CTRL VSI's Tx queue 0 is reconfigured and
ice_is_txtime_ena() is called for that ring. Since it only checks
pf->txtime_txqs by queue index without distinguishing VSI type, it
finds bit 0 set and returns true, matching the PF VSI's ETF queue,
not the CTRL VSI's. This causes ice_vsi_cfg_txq() to spuriously
allocate a tstamp_ring for the CTRL VSI ring.

Since CTRL VSI rings have no associated netdev, ice_clean_tx_ring()
takes an early return at the !netdev check before reaching
ice_free_tx_tstamp_ring(), leaking the allocation. Each PCI reset
leaks one 64-byte tstamp_ring.

Fix this by restricting ice_is_txtime_ena() to return true only for
PF VSI rings, since txtime_txqs is only meaningful for PF VSI queues.