ifscand 0.4 with OpenBSD 6.1 support

• Compile fixes for OpenBSD 6.1
• Added functionality for "-N" command line flag
• Now builds under /usr/ports/net/ifscand; template is in the ports/ subdir

Initial working version on OpenBSD 6.0

• tested on OpenBSD 6.0/amd64 and iwn
• ifscanctl commands resemble ifconfig(8) options
• ifscand by default only works on the link layer attachment
• ifscand can optionally start dhcp if configured