Allow execution of /system/bin/ip commands.

netmgrd can run ip commands, allow this.
Remove dontaudit rules related to running external helpers.
This will generate some log noise on boot due to
sh -c 'rm /data/data_test/modem_port_status' commands but could
otherwise conceal denied execution of other helper programs.

Change-Id: I4ae3870c3d58a0b39eeb767310b045416265940c
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>