Fix mac_interfaces use in loader.conf.
Fix mac_interfaces use in loader.conf.

This change fixes the code in mfsbsd that expands the
mfsbsd.mac_interfaces variable set in loader.conf. Aside from a typo
that looked at cloned_interfaces, there was also the issue of
correctly quoting $i so that it expands $i rather than $i_mac.

DaElf/mfsbsd,DaElf/mfsbsd,meganuke19/mfsbsd,mmatuska/mfsbsd,johnko/mfsbsd,mmatuska/mfsbsd,johnko/mfsbsd,meganuke19/mfsbsd,solobsd/SoloBSD,solobsd/SoloBSD