Replace assignments to individual fields of wire.NetAddress with
creating the entire object at once, as one would do if the type was
immutable.
In some places this replaces the creation of a NetAddress with a
high-precision timestamp with a call to a 'constructor' that converts
the timestamp to single second precision. For consistency, the tests
have also been changed to use single-precision timestamps.
Lastly, the number of allocations in readNetAddress have been reduced by
reading the services directly into the NetAddress instead of first into
a temporary variable.
This makes two modifications based on the results of staticcheck.
The first is to use a simplified zero value for the time in the addrmgr
package tests.
The second is check any errors when opening a directory while attempting
to perform old version upgrades.
