In SR4, the only real way to "tank" is as Melee. The converse is mostly true - one of the best things you can do as a melee character is tank.
The reasons for this are: a) -3 for firing while in melee. +2 for firing at point blank. This means people are -1 to shoot you, but -3 to shoot other people (and -0 to melee you). This makes people more likely to attack you.
b) Realistically, even if you should be firing at the very pretty elf 30 meters away who's spacing out, most people in the stress of combat will actually shoot at the troll who's in your face with a cyberspur, regardless of whether the troll is objectively the larger threat or not, and many GMs will run it like that.
So there are 3 parts of tanking:
1) Getting into melee
2) Doing enough damage in melee to not be a joke
3) Not dying when you draw fire from everyone.
It's also not a bad idea to not suck too bad at range combat, just so you can do something when nobody is on the ground or near you. You probably want longer-range range weapons.
1) is best solved by being a troll and having Cyberskates. In addition to giving you a high movement, this makes you a troll who skates into battle. How dark eighties future is that?
2) is best solved by being at troll with one or more cyberlimbs that have either Cyberspurs (arms) or Foot Anchors (feet).
3) is best solved by being a troll with as many cyberlimbs as you can jam on, and having (among other things) Armor on them, and using them to average up your Body score. Then wearing a bunch of armor on top of that.
I assume you can see where this is going; you pretty much want to be Robotroll. Robo-ork, Robo-elf, and Robo-human also work A-OK.
EDIT: With core only, Foot Anchors and Cyberskates are right out, but the rest of this works fine.
