usb: gadget: net2280: don't connect from udc_start

net2280_start can be called with pullup disabled. Don't set
softconnect flag in it. Let net2280_pullup handle the connection part.

Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>