libnm: hash settings in NMConnection by gtype

NMConnection keeps a list (hash table) of all settings.

There are two lookup methods to find a setting in a connection:

  - nm_connection_get_setting() by GType
  - nm_connection_get_setting_by_name() by name

Note, that nm_connection_get_setting_by_name() first converts the
name to a GType, and then looks up the setting by GType.

But theni, it would again convert the GType to the type name, and
hash the name. That is pointless, just index by type directly.

Maybe, using a hash table is anyway overkill because commonly there are
only a handful of settings in a connection. Regardless of that, change
the hashing.
5 jobs for th/setting-hash in 58 minutes and 27 seconds (queued for 166 minutes and 15 seconds)