examples/vm_power: drop Unix path limit redefinition

examples/vm_power: drop Unix path limit redefinition

The Unix socket path may be as long as UNIX_PATH_MAX.
This constant is supposed to be defined in sys/un.h.
On Linux, it appears to be in linux/un.h.

This constant was re-defined locally, based on a variable declaration.
It is breaking compilation with -fno-common (default in GCC 10)
We could avoid the variable declaration by using NULL struct,
but it looks simpler not redefining this system constant.

As the power library and its examples are restricted to Linux only,
the Linux header file is directly included.

Fixes: 0d74597c1b4f ("examples/vm_power: fix max length of unix socket path")
Cc: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: David Marchand <david.marchand@redhat.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>