There is no "prescriptive easement" or "adverse possession" involved in the situation that you describe. If the porch was built before the setback requirement came into effect, it would be "grandfathered." Otherwise, it is just an existing code violation which is subject to enforcement.
I generally agree with Mr. Daudt's advice. I would add, however, depending upon how recently the property has been surveyed, there could "possibly" be an easement issue. I would also investigate to determine if any easement has been recorded since the purchase. Good luck.
As I understand the facts as you outlined, the neighbor's porch is built up to the property line --- it does not encroach on your property. If that is the case, then you would not expect to find an easement recorded on your property. If you are concerned that the location of the porch in relation to the property line may be a zoning violation, you should contact your city or County code enforcement office. As an aside, this may not be the best action to facilitate good neighbor relations.
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