defconfig: arm64: sdm855: Enable rmnet driver

RmNet driver enables a transport agnostic MAP (multiplexing and
aggregation protocol) data support. rmnet provides virtual network
devices which can be attached to any IP-mode physical device.

CRs-Fixed: 2156182
Change-Id: I4457ec1fdc99ea34b39931a634543f5f67c8cfdd
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>