[FS#1037] netifd: implement point-to-point interface support

[LEDE Bugs]

The following task is now closed:

FS#1037 - netifd: implement point-to-point interface support
User who did this - Hans Dedecker (dedeckeh)

Reason for closing: Implemented
Additional comments about closing: Point-to-Point IPv4 address config support added in https://git.lede-project.org/?p=project/netifd.git;a=commit;h=0f96606b7040b8e14190ff055d5761744bc15f6d

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=1037