net: qualcomm: rmnet: Refactor uplink aggregation

Move the config setting and the allocation into a helper function.
This can be reused for any newer operations.

CRs-Fixed: 2512312
Change-Id: I13392f6ded973d8d07bcb8e19a7dd9535e60d005
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>