Optimize macAddressToBytes()

Using raw string parsing has some significant overhead. For parsing a
MAC address, we can employ hand-coded routing which has does not
allocate objects and is much more (~140x) more efficient.

Change-Id: Iad1e6bc1618dd1eedcdfbc9f1e55ac49d03ea4aa
Signed-off-by: Robert Varga <rovarga@cisco.com>