lime-system: activate mesh_nolearn

[a-gave]

Closes #1232

Set the wifi option ieee80211s_mesh_nolearn='1' in lime-defaults in a similar way to how ieee80211s_mesh_fwding is set to 0.

[ilario]

Just for me to remember how these options work:
They get parsed here and passed to the mode:

lime-packages/packages/lime-system/files/usr/lib/lua/lime/wireless.lua

Lines 228 to 251 in c95c7bc

	--! gather mode specific configs (eg ieee80211s_mcast_rate_5ghz)
	for key,value in pairs(options) do
	local keyPrefix = utils.split(key, "_")[1]
	local isGoodOption = ( (key ~= "modes")
	and (not key:match("^%."))
	and (not key:match("channel"))
	and (not key:match("country"))
	and (not key:match("legacy_rates"))
	and (not key:match("txpower"))
	and (not key:match("htmode"))
	and (not key:match("distance"))
	and (not key:match("unstuck_interval"))
	and (not key:match("unstuck_timeout"))
	and (not (wireless.isMode(keyPrefix) and keyPrefix ~= modeName)))
	if isGoodOption then
	local nk = key:gsub("^"..modeName.."_", "")
	if nk == "ssid" then
	value = wireless.resolve_ssid(value)
	end
	args[nk] = value
	end
	end
	mode.setup_radio(radio, args)

The edit is justified in #1232 and the code edit seems safe. I didn't manage to test but I think this is safe to merge.