net: make vlan_get_tag() return -ENODATA instead of -EINVAL

JIRA: https://issues.redhat.com/browse/RHEL-31890

Upstream commit(s):
commit 537fec0
Author: Larysa Zaremba <larysa.zaremba@intel.com>
Date:   Tue Dec 5 22:08:42 2023 +0100

    net: make vlan_get_tag() return -ENODATA instead of -EINVAL

    __vlan_hwaccel_get_tag() is used in veth XDP hints implementation,
    its return value (-EINVAL if skb is not VLAN tagged) is passed to bpf code,
    but XDP hints specification requires drivers to return -ENODATA, if a hint
    cannot be provided for a particular packet.

    Solve this inconsistency by changing error return value of
    __vlan_hwaccel_get_tag() from -EINVAL to -ENODATA, do the same thing to
    __vlan_get_tag(), because this function is supposed to follow the same
    convention. This, in turn, makes -ENODATA the only non-zero value
    vlan_get_tag() can return. We can do this with no side effects, because
    none of the users of the 3 above-mentioned functions rely on the exact
    value.

    Suggested-by: Jesper Dangaard Brouer <jbrouer@redhat.com>
    Acked-by: Stanislav Fomichev <sdf@google.com>
    Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
    Link: https://lore.kernel.org/r/20231205210847.28460-14-larysa.zaremba@intel.com
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Signed-off-by: Petr Oros <poros@redhat.com>

Author: orosp

include/linux/if_vlan.h

@@ -543,7 +543,7 @@ static inline int __vlan_get_tag(const struct sk_buff *skb, u16 *vlan_tci)
 	struct vlan_ethhdr *veth = skb_vlan_eth_hdr(skb);
 
 	if (!eth_type_vlan(veth->h_vlan_proto))
-		return -EINVAL;
+		return -ENODATA;
 
 	*vlan_tci = ntohs(veth->h_vlan_TCI);
 	return 0;
@@ -564,7 +564,7 @@ static inline int __vlan_hwaccel_get_tag(const struct sk_buff *skb,
 		return 0;
 	} else {
 		*vlan_tci = 0;
-		return -EINVAL;
+		return -ENODATA;
 	}
 }