Improve IptablesRestoreController error logging.

- Switch tag from /system/bin/netd to IptablesController for
  consistency.
- When a command fails, include the command that caused the error
  in addition to the error itself.

Example output:

02-03 16:35:01.044 17129 17129 E IptablesRestoreController: iptables error:
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: ------- COMMAND -------
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: *filter
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: :natctrl_tether_counters -
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: badbadbadbad
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: COMMIT
02-03 16:35:01.044 17129 17129 E IptablesRestoreController:
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: ------- ERROR -------
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: Bad argument `badbadbadbad'
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: Error occurred at line: 112
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: Try `ip6tables-restore -h' or 'ip6tables-restore --help' for more information.
02-03 16:35:01.044 17129 17129 E IptablesRestoreController: ----------------------

Test: added an invalid command to NatController, observed above log messages
Bug: 32323979
Change-Id: I0c1c37464f5b19c64d6e043aef8704285df4c508