Revert "[connman] network: protect service structure access with reference"

This reverts commit 6c67f39167ed6e3f2ace85d13d3507b32a2cb06b.
connection: Clean up service reference counting

Always reference a service when it is added to the hash and
unreference it when removed. When re-adding gateway data, the
included service is first referenced a second time whereafter
one reference is dropped as g_hash_table_replace() is removing
the previously existing entry.
Merge pull request #178 from hmallat/refix-service-access-protection

Refix service access protection