rpcclient: Parsing received notifications should not check for exact number of positional parameters

[davecgh]

From @jrick on January 25, 2017 16:8

This makes backwards compatibility impossible when it could be since it prevents the addition of other parameters passed in the notification in later versions of the API. Instead, it should check that there are at least the expected number of parameters.

Copied from original issue: btcsuite/btcrpcclient#115