network: network_do_splice(): Set error code
network: network_do_splice(): Set error code

If splice() returns an error propagate the error value instead of returning
-1.

Signed-off-by: Lars-Peter Clausen <3318dc5ce3e4fb7c28a0b841b6801c884e1d0896@metafoo.de>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio