app/testpmd: fix build with gcc 11

app/testpmd: fix build with gcc 11

Error observed with gcc 11 under development
gcc (GCC) 11.0.0 20200920 (experimental)

../app/test-pmd/config.c:1777:61:
	warning: argument 3 of type ‘const uint32_t[n]’
	{aka ‘const unsigned int[n]’} declared as a variable length
	array [-Wvla-parameter]
 1777 | port_flow_list(portid_t port_id, uint32_t n,
 			const uint32_t group[n])
      |                 ~~~~~~~~~~~~~~~^~~~~~~~
In file included from ../app/test-pmd/config.c:53:
../app/test-pmd/testpmd.h:764:67:
	note: previously declared as a pointer ‘const uint32_t *’
	{aka ‘const unsigned int *’}
  764 | void port_flow_list(portid_t port_id, uint32_t n,
  				const uint32_t *group);
      |                         ~~~~~~~~~~~~~~~~^~~~~

Fixes: 938a184a1870 ("app/testpmd: implement basic support for flow API")
Cc: stable@dpdk.org
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Asaf Penso <asafp@nvidia.com>