Remove addressof from the client chain

[xzfc]

The issue with the old code (simplified for the clarity):

var rv networkservice.NetworkServiceClient
onHeal = addressof.NetworkServiceClient(rv)
rv = something()

// Now, *onHeal == nil, which isn't expected

This code is an equivalent to the following:

var rv networkservice.NetworkServiceClient
client := rv
onHeal = &client
rv = something()

// Now, *onHeal == nil, which isn't expected

The new code:

var rv networkservice.NetworkServiceClient
onHeal = &rv
rv = something()

// *onHeal == rv, as expected

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Related: #534 (comment)
This is not the only instance where a similar issue with addressof occurs, I'll address the others in a separate issue.