net/tap: allow user MAC to be passed as args

net/tap: allow user MAC to be passed as args

Allow TAP PMD to pass user desired MAC address as argument.
The argument value is processed as string delimited by  ':',
is parsed and converted to HEX MAC address after validation.

Signed-off-by: Vipin Varghese <vipin.varghese@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Pascal Mazon <pascal.mazon@6wind.com>