Fix taskstats for libnl

taskstats doesn't work, probably caused by when I switched it from
using system/core/libnl_2 to external/libnl.  Fix a few bugs that
libnl_2 didn't care about:
 - callbacks must be registered with NL_CB_CUSTOM
 - nla_next is not guaranteed to work if !nla_ok, use nla_for_each_attr
   which does the right thing
 - instead of fixing get_family_id, use genl_ctrl_resolve
 - instead of manually setting pid, seq, and flags, use
   nl_send_auto_complete
 - since there is now only one command sent, get rid of send_command
   and take advantage of the known parameter type to use nla_put_u32
 - libnl does not set errno, return nl error codes and use nl_perror
   instead of perror

Change-Id: Ic631c8c1d9cc6ed288cbbeb6fe40c45ca5fe9143
1 file changed