system-linux: make encaplimit configurable for ip6 tunnels (FS#1501)
Make encapsulation limit of IP6 tunnels configurable for the ds-lite/map
proto shell handlers as not all ISPs support the destination option header
containing the tunnel encapsulation limit value as reported in FS#1501.
The IP6 tunnel specific setting encaplimit is parsed as a nested json
data object; setting it to ignore disables the insertion of the
destination option header while a value from 0 till 255 sets the
tunnel encapsulation limit accordingly in the destination option header.
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>