public/netd.te: allow netd to operate icmp_socket that passed to it

This should be supplement for the change here:
https://android-review.googlesource.com/c/platform/system/sepolicy/+/708638



When test the cts libcore.libcore.io.OsTest#test_socketPing test case, it will fail
with avc denial message like following:

[ 1906.617027] type=1400 audit(1530527518.195:10496): avc: denied { read write } for comm="netd" path="socket:[32066]" dev="sockfs" ino=32066 scontext=u:r:netd:s0 tcontext=u:r:untrusted_app:s0:c512,c768 tclass=icmp_socket permissive=1
[ 1906.617189] type=1400 audit(1530527518.195:10496): avc: denied { read write } for comm="netd" path="socket:[32066]" dev="sockfs" ino=32066 scontext=u:r:netd:s0 tcontext=u:r:untrusted_app:s0:c512,c768 tclass=icmp_socket permissive=1
[ 1906.617206] type=1400 audit(1530527518.195:10497): avc: denied { getopt } for comm="netd" lport=2 scontext=u:r:netd:s0 tcontext=u:r:untrusted_app:s0:c512,c768 tclass=icmp_socket permissive=1
[ 1906.617313] type=1400 audit(1530527518.195:10497): avc: denied { getopt } for comm="netd" lport=2 scontext=u:r:netd:s0 tcontext=u:r:untrusted_app:s0:c512,c768 tclass=icmp_socket permissive=1
[ 1906.617330] type=1400 audit(1530527518.195:10498): avc: denied { setopt } for comm="netd" lport=2 scontext=u:r:netd:s0 tcontext=u:r:untrusted_app:s0:c512,c768 tclass=icmp_socket permissive=1
[ 1907.832425] type=1400 audit(1530527518.195:10498): avc: denied { setopt } for comm="netd" lport=2 scontext=u:r:netd:s0 tcontext=u:r:untrusted_app:s0:c512,c768 tclass=icmp_socket permissive=1

Test: run cts -m CtsLibcoreTestCases -t libcore.libcore.io.OsTest#test_socketPing

Change-Id: If41cb804292834b8994333f170d1f7f837bcd7df
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>