Use correct transport type while encrypting link

This patch uses the transport type from the GATT event instead
of using the device type stored in NVRAM, to determine the
transport type while encrypting the link. The issue is seen
with dual mode devices, when the connection on LE transport
causes encryption request on the BR/EDR transport

Bug: 21652097
Change-Id: I895756f9c0048b5a559ea00f633b1100109e52b8