udp: enable UDP checksum offload for ESP

In case NIC has support for ESP TX CSUM offload skb->ip_summed is not
set to CHECKSUM_PARTIAL which results in checksum calculated by SW.

Fix enables ESP TX CSUM for UDP by extending condition with check for
NETIF_F_HW_ESP_TX_CSUM.

Signed-off-by: Jacek Kalwas <[e-mail]>
Signed-off-by: Steffen Klassert <[e-mail]>

net/ipv4/ip_output.c

···
 	    length + fragheaderlen <= mtu &&
 	    rt->dst.dev->features & (NETIF_F_HW_CSUM | NETIF_F_IP_CSUM) &&
 	    !(flags & MSG_MORE) &&
-	    !exthdrlen)
+	    (!exthdrlen || (rt->dst.dev->features & NETIF_F_HW_ESP_TX_CSUM)))
 		csummode = CHECKSUM_PARTIAL;
 
 	cork->length += length;