igc: set tx buffer type for SMD frames

igc: set tx buffer type for SMD frames

Sashiko pointed out that igc_fpe_init_smd_frame() initializes
igc_tx_buffer fields for an SMD skb, but does not set the buffer type:
https://sashiko.dev/#/patchset/20260415025226.114115-1-kohei%40enjuk.jp

Since igc_tx_buffer entries are reused, a stale XDP or XSK type can
remain and make TX completion use the wrong cleanup path.

Set the buffer type to IGC_TX_BUFFER_TYPE_SKB.

Fixes: 5422570c0010 ("igc: add support for frame preemption verification")
Signed-off-by: Kohei Enju <kohei@enjuk.jp>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20260515182419.1597859-9-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>