Fix core dump when invalid MAC is configured

When configuring an invalid MAC, a runtime error is thrown
with the existing implementation, which causes a core dump
and phosphor-networkd does not respond when further requests
are made.

This commit avoids the core dump that's caused.

Signed-off-by: Asmitha Karunanithi <asmitk01@in.ibm.com>
Change-Id: I5cb5a25e91a685e1bb2f4bb80d3d8f8c483f56a1
3 files changed