Some/most devices implementing gso_partial need to disable the GSO partial
features when the IP ID can't be mangled; to that extend each of them
implements something alike the following:

        if (skb->encapsulation && !(features & NETIF_F_TSO_MANGLEID))
                features &= ~NETIF_F_TSO;

in the ndo_features_check() op, which leads to a bit of duplicate code.

Later patch in the series will implement GSO partial support for virtual
device, and the current status quo will require more duplicate code and
a new indirect call in the TX path for such devices.

Introduce the mangleid_features mask, allowing the core to disable NIC
features based on/requiring MANGLEID, without any further intervention
from the driver.

The same functionality could be alternatively implemented adding a single
boolean flag to the struct net_device, but would require an additional
checks in ndo_features_check().

Also note that the above mentioned action is incorrect if the NIC
additionally implements NETIF_F_GSO_UDP_L4, mangleid_features
transparently handle even such a case.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/linux/netdevice.h | 5 ++++-
 net/core/dev.c            | 4 +++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d99b0fbc1942..23a698b70de1 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h

@@ -1830,7 +1830,9 @@ enum netdev_reg_state {
  *                             and drivers will need to set them appropriately.
  *
  *     @mpls_features: Mask of features inheritable by MPLS
- *     @gso_partial_features: value(s) from NETIF_F_GSO\*
+ *     @gso_partial_features: value(s) from NETIF_F_GSO
+ *     @mangleid_features:     Mask of features requiring MANGLEID, will be
+ *                             disabled together with the latter.
  *
  *     @ifindex:       interface index
  *     @group:         The group the device belongs to

@@ -2219,6 +2221,7 @@ struct net_device {
        netdev_features_t       vlan_features;
        netdev_features_t       hw_enc_features;
        netdev_features_t       mpls_features;
+       netdev_features_t       mangleid_features;

        unsigned int            min_mtu;
        unsigned int            max_mtu;

diff --git a/net/core/dev.c b/net/core/dev.c
index c711da335510..6154f306ed76 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -3788,8 +3788,10 @@ static netdev_features_t gso_features_check(const struct sk_buff *skb,
                struct iphdr *iph = skb->encapsulation ?
                                    inner_ip_hdr(skb) : ip_hdr(skb);

-               if (!(iph->frag_off & htons(IP_DF)))
+               if (!(iph->frag_off & htons(IP_DF))) {
                        features &= ~NETIF_F_TSO_MANGLEID;