defconfig: arm64: sdm845: Enable RMNET_DATA flow control

RMNET_DATA flow control is required when the physical transport is
experiencing congestion. This back pressure may be either in form
of out of band signaling and calling an IOCTL or through in band
flow control through specific command packet types.

CRs-Fixed: 2043768
Change-Id: Ice6b9b1989ae29c087242fc7386ab01cffddc6cf
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>