map: rename type to maptype (FS#3287)

map: rename type to maptype (FS#3287)

"type" is already used as a common option for all protocols types, so
using the same option name for the map type makes the configuration
ambiguous. Luci in particular adds controls for both options and sees
errors when reading the resulting configuration.

Use "maptype" instead, but still fallback to "type" if "maptype" is not
set. This allows configurations to migrate without breaking old
configurations.

This addresses FS#3287.

Signed-off-by: Remi NGUYEN VAN <remi.nguyenvan+openwrt@gmail.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com> [PKG_RELEASE increase]