net: if: Repack net_if_addr struct to save space

Shuffle the fields to different order in net_if_addr struct.
This saves space in net_if struct. This saved 4.8% memory,
640 bytes in original versus 608 bytes after this commit, when
allocating net_if using minimal amount of address counts and
IPv4, DHCPv4 and IPv6 enabled.

Change-Id: I591543cded587178cf6f82189953bb2e99c2188a
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>