Core/Player: Fix armor calculation

Base armor value from WDB data includes the ArmorDamageModifier. Items of
same item level, required level, armor type and equiptment slot should
have (nearly) the same armor values.

See following links for further proofs:
http://pastebin.com/fqNJLYj4
http://www.wowhead.com/item=50466#comments:id=889035:reply=444786

The shown item should have a base armor value of 177 as similar items and
a bonus armor value of 560 which equals 737 - like in DB atm.