usb: gadget: f_gsi: Set MBIM NTB default size in bind_config

Some hosts like Ubuntu does not send USB_CDC_SET_NTB_INPUT_SIZE
for setting NTB size for in endpoint. Hence update ntb_input_size
to default value in bind_config.

Change-Id: I9cb04d28c466069b5b992079199455a61a35a3b9
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>