Avoid searching for the knetattach service on startup

Avoid searching for the knetattach service on startup

The installed services might change while Dolphin is running, so it is
better to only search when they are actually needed instead.

The very first time such a search happens (e.g. after updating the
system), is also somewhat slow, which could slow down the very first
Dolphin startup.

This commit might also produce a very slight general startup speed
improvement. However, the measured change is within the margin of
error.