OffloadUtils - simplify netlink socket lifetime

None of this stuff is performance critical enough that we can't afford
to simply create a new clean netlink socket, and this significantly
simplifies things and makes it all much more thread-safe.

Test: builds, atest
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: If1000d3cead66631d524cb48d581c0f6e53f6d50