Rework of ofp_print_mac() interface

[semihalf-berestovskyy-andriy]

Note: the issue was created automatically with bugzilla2github tool

Bugzilla Bug ID: 71

Date: 2015-11-13 12:07:07 +0100
From: Sorin Vultureanu <sorin.vultureanu@enea.com>
To: Sorin Vultureanu <sorin.vultureanu@enea.com>

Last updated: 2015-11-13 12:07:07 +0100

Bugzilla Comment ID: 99

Date: 2015-11-13 12:07:07 +0100
From: Sorin Vultureanu <sorin.vultureanu@enea.com>

Functionality issue:
This function can be called from two threads and provide ok results. If you call it and use it from 3 threads in the same time then it would provide bad results.

ofp_print_mac() interface is kinda unusual:
A normal usage would be:

char print_mac[24];
printf ("mac:%s\n", ofp_print_mac(mac, print_mac));

New interface proposal would be:
char ofp_print_mac(uint8_t mac, char* printed_mac);

If printed_mac is NULL then the functionality is as now.
If printed_mac is valid then use this address to store mac and also return it as return value.