soc: qcom: qmi: add CONFIG_NET dependency

Access to the socket API and the root network namespace is only available
when networking is enabled:

ERROR: "kernel_sendmsg" [drivers/soc/qcom/qmi_helpers.ko] undefined!
ERROR: "sock_release" [drivers/soc/qcom/qmi_helpers.ko] undefined!
ERROR: "sock_create_kern" [drivers/soc/qcom/qmi_helpers.ko] undefined!
ERROR: "kernel_getsockname" [drivers/soc/qcom/qmi_helpers.ko] undefined!
ERROR: "init_net" [drivers/soc/qcom/qmi_helpers.ko] undefined!
ERROR: "kernel_recvmsg" [drivers/soc/qcom/qmi_helpers.ko] undefined!

Adding a dependency on CONFIG_NET lets us build it in all randconfig
builds.

Fixes: 9b8a11e8 ("soc: qcom: Introduce QMI encoder/decoder")
Acked-by: Andy Gross <andy.gross@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>