16884 viona TSO should better handle csum offloads

@@ -34,10 +34,11 @@
  * http://www.illumos.org/license/CDDL.
  *
  * Copyright 2015 Pluribus Networks Inc.
  * Copyright 2019 Joyent, Inc.
  * Copyright 2024 Oxide Computer Company
+ * Copyright 2024 MNX Cloud, Inc.
  */
 
 
 #include <sys/types.h>
 #include <sys/smt.h>

@@ -382,13 +383,13 @@
         /*
          * We ignore hdr_len because the spec says it can't be
          * trusted. Besides, our own stack will determine the header
          * boundary.
          */
-        if ((link->l_cap_csum & HCKSUM_INET_PARTIAL) != 0 &&
-            (hdr->vrh_gso_type & VIRTIO_NET_HDR_GSO_TCPV4) != 0 &&
+        if ((hdr->vrh_gso_type & VIRTIO_NET_HDR_GSO_TCPV4) != 0 &&
             ftype == ETHERTYPE_IP) {
+                if ((link->l_cap_csum & HCKSUM_INET_PARTIAL) != 0) {
                 uint16_t        *cksump;
                 uint32_t        cksum;
                 ipaddr_t        src = ipha->ipha_src;
                 ipaddr_t        dst = ipha->ipha_dst;
 

@@ -409,10 +410,11 @@
                 cksum = IP_TCP_CSUM_COMP;
                 cksum += (dst >> 16) + (dst & 0xFFFF) +
                     (src >> 16) + (src & 0xFFFF);
                 cksum = (cksum & 0xFFFF) + (cksum >> 16);
                 *(cksump) = (cksum & 0xFFFF) + (cksum >> 16);
+                }
 
                 /*
                  * Since viona is a "legacy device", the data stored
                  * by the driver will be in the guest's native endian
                  * format (see sections 2.4.3 and 5.1.6.1 of the