Commit 5cd88f4 "dnsmasq: remove use of uci state for getting network ifname"
broke the ability to specify unmanaged network device names for inclusion
and exclusion in the uci configuration.
Restore support for raw device names by falling back to the input value
when "network_get_device" yields no result.
Fixes FS#876.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>