dpdk/eal: fix secondary process calling eal_bus_cleanup() (#860)

Secondary processes (e.g. ff_ifconfig, ff_sysctl) should not invoke
eal_bus_cleanup() on exit, because it calls drv->remove() on every PCI
device.  For the virtio PMD this eventually reaches virtio_reset(), which
writes VIRTIO_CONFIG_STATUS_RESET (0x00) to the device status register
and resets the NIC hardware.  The primary process (F-Stack / nginx) loses
its NIC after that and stops accepting new connections.

Root cause: commit 1cab1a40ea9b ("bus: cleanup devices on shutdown",
DPDK 22.11) added eal_bus_cleanup() to rte_eal_cleanup() without
distinguishing primary from secondary processes.

Fix: guard eal_bus_cleanup() with a primary-process check, identical to
the approach in upstream DPDK commit 4bc53f8f0d64 ("eal: fix MP socket
cleanup", merged for DPDK 25.07).  Backported here for the bundled
DPDK 23.11.5.

Fixes: #860

Author: jfb8856606

dpdk/lib/eal/linux/eal.c

@@ -1370,7 +1370,18 @@ rte_eal_cleanup(void)
 	vfio_mp_sync_cleanup();
 #endif
 	rte_mp_channel_cleanup();
-	eal_bus_cleanup();
+	/* Secondary processes should not call eal_bus_cleanup() because it
+	 * invokes drv->remove() on all PCI devices, which for virtio PMD ends
+	 * up calling virtio_reset() and writing VIRTIO_CONFIG_STATUS_RESET to
+	 * the hardware.  This resets the NIC owned by the primary process,
+	 * causing it to stop accepting new connections.
+	 *
+	 * Upstream fix: commit 4bc53f8f0d64 ("eal: fix MP socket cleanup"),
+	 * DPDK >= 25.07.  Backport for F-Stack bundled DPDK 23.11.5.
+	 * See also: https://github.com/F-Stack/f-stack/issues/860
+	 */
+	if (rte_eal_process_type() == RTE_PROC_PRIMARY)
+		eal_bus_cleanup();
 	rte_eal_alarm_cleanup();
 	rte_trace_save();
 	eal_trace_fini();