sys/net: add VAINA configuration interface

[jeandudey]

This adds a configuration interface to add clients to the Router Client Set, in the future the VAINA (vaina as of now) will be extended to support other features, it can only be used over SLIP, messages should be sent to if local multicast address ff01::1

VAINA stands for VAINA - Versatile Address Interface | Network Administration.

[luisan00]

configuring a custom SLIP LOCAL_ADDR should be an option in themenuconfig

[jeandudey]

configuring a custom SLIP_LOCAL_ADDR should be an option in the menuconfig

I'll try to do it, there are some limitations by having it in menuconfig

[jeandudey]

Comments addressed, please review.

[luisan00]

Travis looks unhappy =(

[jeandudey]

@luisan00 looks like the connection died when downloading GCC, I restarted the build and I hope It will survive next time.

[luisan00]

I will pray for him

[jeandudey]

Commits squashed for easy review of each one.