igc: fix potential skb leak in igc_fpe_xmit_smd_frame()

igc: fix potential skb leak in igc_fpe_xmit_smd_frame()

When igc_fpe_init_tx_descriptor() fails, no one takes care of an
allocated skb, leaking it. [1]
Use dev_kfree_skb_any() on failure.

Tested on an I226 adapter with the following command, while injecting
faults in igc_fpe_init_tx_descriptor() to trigger the error path.
 # ethtool --set-mm $DEV verify-enabled on tx-enabled on pmac-enabled on

[1]
unreferenced object 0xffff888113c6cdc0 (size 224):
...
  backtrace (crc be3d3fda):
    kmem_cache_alloc_node_noprof+0x3b1/0x410
    __alloc_skb+0xde/0x830
    igc_fpe_xmit_smd_frame.isra.0+0xad/0x1b0
    igc_fpe_send_mpacket+0x37/0x90
    ethtool_mmsv_verify_timer+0x15e/0x300

Cc: stable@vger.kernel.org
Fixes: 5422570c0010 ("igc: add support for frame preemption verification")
Signed-off-by: Kohei Enju <kohei@enjuk.jp>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20260515182419.1597859-10-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>