We also make use of the boolean support of simple-uci to make scripts
clearer.

gluon-client-bridge: add LAN interfaces to client bridge by default (instead of doing this in the batman-adv-specific scripts)

This allows to weaken the gluon-mesh-batman-adv-core dependency of
gluon-luci-portconfig to gluon-client-bridge.

Fixes #328

Make bandwidth limits unsigned; trim numbers, the validator accepts
trailing whitespace.

gluon-mesh-batman-adv-core/gluon-luci-portconfig: fix configuration of br-client ifname with multiple interfaces in lan_ifname

There are a few devices on which lan_ifname contains multiple interface
names separated by spaces.

Convert option ifname in br-client to use a list instead. This
simplifies adding and remove interfaces:

uci:add_to_set("network", "client", "ifname", "eth0")
uci:remove_from_set("network", "client", "ifname", "eth0")

An option ifname will be automatically converted to a list when
performing an upgrade.

Packages affected: gluon-mesh-batman-adv-core, gluon-luci-portconfig