tools/compat: add root privilege check in ff_ipc_init()

[jfb8856606]

Summary

F-Stack tools (ifconfig, netstat, ipfw, arp, etc.) are DPDK secondary processes and must be run as root. When executed as a non-root user, DPDK uses a per-user runtime directory (/run/user/<uid>/dpdk/) instead of the system-wide /var/run/dpdk/, causing a cryptic and misleading error:

EAL: Cannot open '/run/user/1000/dpdk/rte/config' for rte_mem_config
EAL: FATAL: Cannot init config
EAL: Error - exiting with code: 1
  Cause: Error with EAL initialization

This change adds an explicit root privilege check at the start of ff_ipc_init(), printing a clear and actionable error message before DPDK initialization is attempted.

Change

Add to tools/compat/ff_ipc.c, in ff_ipc_init():

if (getuid() != 0) {
    rte_exit(EXIT_FAILURE, "Error: F-Stack tools must be run as root.\n");
}

Before / After

Before (as non-root):

EAL: Cannot open '/run/user/1000/dpdk/rte/config' for rte_mem_config
EAL: FATAL: Cannot init config
EAL: Error - exiting with code: 1
  Cause: Error with EAL initialization

After (as non-root):

PANIC in ff_ipc_init():
Error: F-Stack tools must be run as root.

Fixes #829.