app/testpmd: fix build without drivers

[ upstream commit 1a2eaef ]

When ixgbe and bnxt are disabled, compilation was failing:

app/test-pmd/cmdline.c:9396:11: error:
	variable 'vf_rxmode' set but not used

Fixes: 4cfe399 ("net/bnxt: support to set VF rxmode")

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>

app/test-pmd/cmdline.c

@@ -8739,6 +8739,7 @@ cmd_set_vf_rxmode_parsed(void *parsed_result,
 	}
 
 	RTE_SET_USED(is_on);
+	RTE_SET_USED(vf_rxmode);
 
 #ifdef RTE_NET_IXGBE
 	if (ret == -ENOTSUP)