luci-mod-status: use network.getDSLModemType()

This matches what luci-mod-network does for the DSL modem configuration.

Since this is based on a common uci config, it may also prevent issues as
fixed with 111c551c

 "luci-base: fix DSL feature detection" in the future.

Signed-off-by: Andre Heider <a.heider@gmail.com>