msm: emac: Add BQL support

Change driver transmit to support Byte Queue Limit (BQL). Warning about
receive errors is removed.

Change-Id: Ic57b602819b0a994264abb78b31387482a4c9c58
Acked-by: Jie Luo <jluo@qti.qualcomm.com>
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>