map: drop default encaplimit value

map: 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 map connectivity.
Therefore drop the default encaplimit value for map tunnels so
no destination option header is included by default.

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>
(backported from d9691b66e2781a43cd4f508605dcfe88c4bbd042)