msm: ipa: allow dtsi based lan rx ring size

Add support for specifying the size of LAN RX buffer pool.
Once this specified in dtsi, it will override the default value.

Change-Id: I60ff9ecf7e27aa9cd20dbc693e2ac392c401dfb9
CRs-Fixed: 1050748
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>