util: netlink: define cleanup function using VIR_DEFINE_AUTOPTR_FUNC

util: netlink: define cleanup function using VIR_DEFINE_AUTOPTR_FUNC

Using the new VIR_DEFINE_AUTOPTR_FUNC macro defined in
src/util/viralloc.h, define a new wrapper around an existing
cleanup function which will be called when a variable declared
with VIR_AUTOPTR macro goes out of scope. Also, drop the redundant
viralloc.h include, since that has moved from the source module into
the header.

This commit also typedefs virNetlinkMsg to struct nl_msg type for use
with the cleanup macros.

When a variable of type virNetlinkMsg * is declared using VIR_AUTOPTR,
the function nlmsg_free will be run automatically on it when it
goes out of scope.

Signed-off-by: Sukrit Bhatnagar <skrtbhtngr@gmail.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>