ip6gretap encapsulation-limit missing "none" value

Hello, creating an ip6gretap ip-tunnel using ip command we are allowed to set either "none" or a numerical value

#ip link add g6m type ip6gretap help
Usage: ... ip6gretap   
(...)
                        [ encaplimit ELIM ]
(...)
Where:  ADDR      := IPV6_ADDRESS
        TTL       := { 0..255 } (default=64)
        KEY       := { DOTTED_QUAD | NUMBER }
        ELIM      := { none | 0..255 }(default=4)  <<<<
        TCLASS    := { 0x0..0xff | inherit }
        FLOWLABEL := { 0x0..0xfffff | inherit }
        MARK      := { 0x0..0xffffffff | inherit }

But creating via nmcli forces to use a numerical value only.

# nmcli c modify ip-tunnel ip-tunnel.encapsulation-limit none
Error: failed to modify ip-tunnel.encapsulation-limit: 'none' is not a valid number.

If a numerical value is set, IPv6 packet will have DST-options header which is used to store the encaplimit. If "none" value is set, DST-Options header is not used. Some implementations don't support IPv6 DST-Options, therefore is important the ability to set to "none".