selftests: net: check jq command is supported

The jq command is used in vlan_bridge_binding.sh, if it is not supported,
the test will spam the following log.

# ./vlan_bridge_binding.sh: line 51: jq: command not found
# ./vlan_bridge_binding.sh: line 51: jq: command not found
# ./vlan_bridge_binding.sh: line 51: jq: command not found
# ./vlan_bridge_binding.sh: line 51: jq: command not found
# ./vlan_bridge_binding.sh: line 51: jq: command not found
# TEST: Test bridge_binding on->off when lower down [FAIL]
# Got operstate of , expected 0

The rtnetlink.sh has the same problem. It makes sense to check if jq is
installed before running these tests. After this patch, the
vlan_bridge_binding.sh skipped if jq is not supported:

# timeout set to 3600
# selftests: net: vlan_bridge_binding.sh
# TEST: jq not installed [SKIP]

Fixes: dca12e9ab760 ("selftests: net: Add a VLAN bridge binding selftest")
Fixes: 6a414fd77f61 ("selftests: rtnetlink: Add an address proto test")
Signed-off-by: Wang Liang <[e-mail]>
Reviewed-by: Hangbin Liu <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

tools/testing/selftests/net/rtnetlink.sh

···
 EOF
 }
 
+require_command jq
+
 #check for needed privileges
 if [ "$(id -u)" -ne 0 ];then
 	end_test "SKIP: Need root privileges"

tools/testing/selftests/net/vlan_bridge_binding.sh

···
 	do_test_binding_off : "on->off when upper down"
 }
 
+require_command jq
+
 trap defer_scopes_cleanup EXIT
 setup_prepare
 tests_run