core: unblock signals for child processes we spawn out of NM (rh #739836)

Commit 217c5bf6ac fixed processing of unix
signals: signals are blocked in all threads and a dedicated thread handles the
signals using sigwait().
However, the commit forgot that child processes inherit signal mask as well.
That is why we have to unblock signals for child processes we spawn from NM, so
that they can receive signals.

src/nm-activation-request.c

@@ -36,6 +36,7 @@
 #include "nm-device.h"
 #include "nm-active-connection.h"
 #include "nm-settings-connection.h"
+#include "nm-posix-signals.h"
 
 
 G_DEFINE_TYPE (NMActRequest, nm_act_request, NM_TYPE_ACTIVE_CONNECTION)
@@ -261,6 +262,8 @@ share_child_setup (gpointer user_data G_GNUC_UNUSED)
 	/* We are in the child process at this point */
 	pid_t pid = getpid ();
 	setpgid (pid, pid);
+
+	nm_unblock_posix_signals (NULL);
 }
 
 void