ds-lite: drop default encaplimit value

ds-lite: drop default encaplimit value

Setting encaplimit to a numerical value results into the value being
included as tunnel encapsulation limit in the destination option header
for tunneled packets.
Several users have reported interop issues as not all ISPs support the
destination option header containing the tunnel encapsulation limit
resulting into broken ds-lite connectivity.
Therefore drop the default encaplimit value for ds-lite tunnels so
no destination option header is included by default.

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>
(backported from 1241707b4091aa9dd46ad75252689e83f6aac5b2)