Values of next-protocol should be:
1 - ipv4
2 - ipv6
3 - Ethernet
4 - NSH
5 - MPLS

However, the values returned by "vxlan_gpe_tunnel_dump" are multiplied by 16777216

create vxlan-gpe tunnel local 192.168.0.2 remote 192.168.1.2 vni 2 next-ip6

vxlan_gpe_tunnel_dump
{
"sw_if_index":3,
"local":"192.168.0.2",
"remote":"192.168.1.2",
"vni":2,
"protocol":33554432,
"encap_vrf_id":0,
"decap_vrf_id":0,
"is_ipv6":0
}