stmmac: Revert "stmmac: align RX buffers"

This reverts commit a955318f ("stmmac: align RX buffers"),
which breaks at least one platform (Nvidia Jetson-X1), causing
packet corruption. This is 100% reproducible, and reverting
the patch results in a working system again.

Given that it is "only" a performance optimisation, let's
return to a known working configuration until we can have a
good understanding of what is happening here.

Fixes: a955318f ("stmmac: align RX buffers")
Cc: Matteo Croce <mcroce@linux.microsoft.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Link: https://lore.kernel.org/netdev/871r71azjw.wl-maz@kernel.orgSigned-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210820183002.457226-1-maz@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -339,9 +339,9 @@ static inline bool stmmac_xdp_is_enabled(struct stmmac_priv *priv)
 static inline unsigned int stmmac_rx_offset(struct stmmac_priv *priv)
 {
 	if (stmmac_xdp_is_enabled(priv))
-		return XDP_PACKET_HEADROOM + NET_IP_ALIGN;
+		return XDP_PACKET_HEADROOM;
 
-	return NET_SKB_PAD + NET_IP_ALIGN;
+	return 0;
 }
 
 void stmmac_disable_rx_queue(struct stmmac_priv *priv, u32 queue);