Avoid leaking file descriptors

Add O_CLOEXEC on open() calls, and SOCK_CLOEXEC on socket calls.
This avoids leaking file descriptors across execs.

Addresses the following SELinux denial:

  audit(1422740213.283:8): avc: denied { read write } for pid=2597 comm="clatd" path="socket:[6709]" dev="sockfs" ino=6709 scontext=u:r:clatd:s0 tcontext=u:r:netd:s0 tclass=netlink_socket

and allows the removal of some other SELinux rules which were
inappropriately added because of leaking file descriptors.

Change-Id: I9c180488ea1969d610e488f967a7276a672bb477
diff --git a/client/FwmarkClient.cpp b/client/FwmarkClient.cpp
index 4e02d58..0ac1fbb 100644
--- a/client/FwmarkClient.cpp
+++ b/client/FwmarkClient.cpp
@@ -43,7 +43,7 @@
 }
 
 int FwmarkClient::send(void* data, size_t len, int fd) {
-    mChannel = socket(AF_UNIX, SOCK_STREAM, 0);
+    mChannel = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
     if (mChannel == -1) {
         return -errno;
     }