tests: use ifindex_lo and IFINDEX_LO_STR

tests: use ifindex_lo and IFINDEX_LO_STR

* tests/netlink_route.c: Do not check for HAVE_IF_INDEXTONAME.
(if_nametoindex, IFINDEX_LO): Remove.
(test_rtnl_link, test_rtnl_addr, test_rtnl_neigh, test_rtnl_tc,
test_rtnl_addrlabel, test_rtnl_mdb): Use ifindex_lo instead
of if_nametoindex, use IFINDEX_LO_STR instead of hardcoded string.
* tests/netlink_sock_diag.c: Do not check for HAVE_IF_INDEXTONAME.
(if_nametoindex, IFINDEX_LO): Remove.
(test_inet_diag_sockid, test_inet_diag_req, test_inet_diag_req_v2,
test_inet_diag_msg, test_smc_diag_req): Use ifindex_lo instead
of if_nametoindex, use IFINDEX_LO_STR instead of hardcoded string.
* tests/nlattr_inet_diag_msg.c: Do not check for HAVE_IF_INDEXTONAME.
(if_nametoindex, IFINDEX_LO): Remove.
(init_inet_diag_msg): Use ifindex_lo instead of if_nametoindex.
(print_inet_diag_msg): Use IFINDEX_LO_STR instead of hardcoded string.
* tests/nlattr_inet_diag_req_compat.c: Do not check
for HAVE_IF_INDEXTONAME.
(if_nametoindex, IFINDEX_LO): Remove.
(init_inet_diag_req): Use ifindex_lo instead of if_nametoindex.
(print_inet_diag_req): Use IFINDEX_LO_STR instead of hardcoded string.
* tests/nlattr_inet_diag_req_v2.c: Do not check for HAVE_IF_INDEXTONAME.
(if_nametoindex, IFINDEX_LO): Remove.
(init_inet_diag_req_v2, print_inet_diag_req_v2,
test_inet_diag_bc_dev_cond): Use ifindex_lo instead of if_nametoindex,
use IFINDEX_LO_STR instead of hardcoded string.
* tests/nlattr_packet_diag_msg.c: Do not check for HAVE_IF_INDEXTONAME.
(if_nametoindex, IFINDEX_LO): Remove.
(main): Use ifindex_lo instead of if_nametoindex.
(print_packet_diag_mclist): Use IFINDEX_LO_STR instead of hardcoded
string.