Make the SocketListener control pipe O_CLOEXEC.

Children of processes that use SocketListener should not be able
to stop the SocketListener.

Test: builds, boots
Test: atest libsysutils_tests
Test: atest --test-mapping system/netd
Bug: 131268436
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I64898d9966f62004468b8e8a43b59be4a81a8cc4
Merged-In: I64898d9966f62004468b8e8a43b59be4a81a8cc4
(cherry picked from commit dae01953)