Make ping enforcing.

Change-Id: Ib43bc4027e74660f653ec90335741acc792739da
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

ping.te

 type ping, domain;
-permissive ping;
 type ping_exec, exec_type, file_type;
 domain_auto_trans(shell, ping_exec, ping)