Change interface filter to cope with interfaces that do not have a hwaddr field

On EC2 (maybe elsewhere too) calls to ```inet:getifaddrs()``` gives an interface that do not have a ```hwaddr``` field. When one of these is encountered the list comprehension in ```filter_if``` returns the empty list which fails the match with ```[HasHwAddr]``` at line 303. 

The block of code that by comments would handle that case never gets reached. This patch matches the whole List rather than the value, meaning that the intended block gets hit with an empty list.