bonding: cleanup bond_create

Setting RLB_NULL_INDEX is not needed as this is done in bond_alb_initialize
which is called by bond_open.

Also reduce the number of rtnl_unlock calls by just using the standard
goto cleanup path.

Signed-off-by: Jonathan Toppins <jtoppins@redhat.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>