selinux: Allow accepting connections on sockets passed from systemd

Otherwise we get AVC's that look like this:

```
type=AVC msg=audit(1402394341.625:70457): avc:  denied  { accept } for  pid=30536 comm="cockpit-ws" lport=1001 scontext=system_u:system_r:cockpit_ws_t:s0 tcontext=system_u:system_r:init_t:s0 tclass=tcp_socket
type=SYSCALL msg=audit(1402394341.625:70457): arch=c000003e syscall=43 success=no exit=-13 a0=3 a1=0 a2=0 a3=1 items=0 ppid=1 pid=30536 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="cockpit-ws" exe="/usr/libexec/cockpit-ws" subj=system_u:system_r:cockpit_ws_t:s0 key=(null)
```