eth: Adjust ENC28J60 MAC configuration.

ENCC28J60 specs section 6.5 "MAC Initialization settings"
state that MACON3(7:5) register configure automatic padding and CRC.
It also states that the configuration 111 and 011 both configure as
all short frames to be zero padded with a valid CRC appended.

Nevertheless, experimentally, there are ocassions when configuring as 111
frames does not have a CRC appended. This frames could be rejected
by the receiver if it is configured to do so.

This commit changes configuration from 111 to 011, which is not
presenting that behavior.

Jira: ZEP-842

Change-Id: I302bb99f7a1f23b298fe0db0245963b640644040
Signed-off-by: Juan Manuel Cruz <juan.m.cruz.alcaraz@intel.com>