tethering: Re-add error message about missing bridge functionality
Commit upstream:
18d852960a02a9939616787043cddea68e92f226
Commit 4fe07df removed an error message about missing bridge functionality.
Return it back.
tethering: Fix bridge module loading problem
Commit upstream:
4fe07dfed4f720136ee142e56a9d43242c8c78dc
Connman tries to check if bridging is supported by the kernel by checking
whether "/proc/sys/net/bridge" is present. If the bridge is a kernel
module which is not already loaded, then tethering cannot be enabled.
Instead of checking for the file we invoke the "get bridge version" socket
ioctl and the kernel will handle module loading issues - if the bridge
module is not loaded, it will first load it, and then check the version.