dns: Remove unused fields from dns_addrinfo struct

The ai_flags, ai_socktype and ai_protocol fields are removed as there
is currently no use for them. These can be added back later if really
needed.
Reordering the fields at the same time which caused 4 bytes to be saved
in storage space.

Jira: ZEP-2065

Change-Id: Ida1dcfb6afed73733d3db9cf4d07e771d31ee314
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>