msm: emac: Properly handle descriptor ring resizing

Resize the descriptor rings only if the interface is up. If the interface
is down, new size will be used when the interface is brought up.

Change-Id: I8d539f202a94631848c10ad7c6b63ee580aaca28
Signed-off-by: Niranjana Vishwanathapura <nvishwan@codeaurora.org>