net: handle ARPHRD_IP6GRE in dev_is_mac_header_xmit()

Similar to commit 3b707c30 ("net: dev_is_mac_header_xmit() true for
ARPHRD_RAWIP"), add ARPHRD_IP6GRE to dev_is_mac_header_xmit(), to make
ip6gre compatible with act_mirred and __bpf_redirect().
Signed-off-by: NGuillaume Nault <gnault@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/if_arp.h

@@ -48,6 +48,7 @@ static inline bool dev_is_mac_header_xmit(const struct net_device *dev)
 	case ARPHRD_TUNNEL6:
 	case ARPHRD_SIT:
 	case ARPHRD_IPGRE:
+	case ARPHRD_IP6GRE:
 	case ARPHRD_VOID:
 	case ARPHRD_NONE:
 	case ARPHRD_RAWIP: