RFC: add hop penalty per hardif setting

[maurerle]

set this using

uci set gluon.mesh_batman_adv.hop_penalty_mesh0='8'

and check using

batctl hardif mesh0 hop_penalty

the sleep somehow is required to wait until the mesh if is up.

I did not find a better way to do this, maybe someone can help here.
If I omit the sleep statement, I get:

Error - invalid hardif mesh0: Link has been severed followed by the batctl help text

• docs are currently missing
• also documentation of gluon.mesh_batman_adv.hop_penalty for the general hop_penalty is not available yet
• requests for improvements on the usage of uci would be cool, but I do not really know, how to do this using a list without the fuzzy string replacement

closes #2754