net: selftests: initialize TCP header and skb payload with zero

net: selftests: initialize TCP header and skb payload with zero

commit 9e8d1013b0c38910cbc9e60de74dbe883878469d upstream.

Zero-initialize TCP header via memset() to avoid garbage values that
may affect checksum or behavior during test transmission.

Also zero-fill allocated payload and padding regions using memset()
after skb_put(), ensuring deterministic content for all outgoing
test packets.

Fixes: 3e1e58d64c3d ("net: add generic selftest support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: stable@vger.kernel.org
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250416160125.2914724-1-o.rempel@pengutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>