vio: Change type of the flags parameter of mowgli_vio_{has,set}flag() to unsigned

The 'flags' in struct _mowgli_vio is unsigned, this causes warnings with -Wsign-conversion
Merge pull request #27 from attilamolnar/vio-warn-fix

vio: Change type of the flags parameter of mowgli_vio_{has,set}flag() to unsigned