zebra: fix pbr_iptable memory leak

zebra: fix pbr_iptable memory leak

We are obviously doing deleting on wrong object.

> Direct leak of 40 byte(s) in 1 object(s) allocated from:
>     #0 0x7fcf718b4a57 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:154
>     #1 0x7fcf7126f8dd in qcalloc lib/memory.c:105
>     #2 0x7fcf7124401a in list_new lib/linklist.c:49
>     #3 0x55771621d86d in pbr_iptable_alloc_intern zebra/zebra_pbr.c:1015
>     #4 0x7fcf71217d79 in hash_get lib/hash.c:147
>     #5 0x55771621dad3 in zebra_pbr_add_iptable zebra/zebra_pbr.c:1030
>     #6 0x55771614d00c in zread_iptable zebra/zapi_msg.c:4131
>     #7 0x55771614e586 in zserv_handle_commands zebra/zapi_msg.c:4424
>     #8 0x5577162dae2c in zserv_process_messages zebra/zserv.c:521
>     #9 0x7fcf7137798e in event_call lib/event.c:2011
>     #10 0x7fcf71242ff1 in frr_run lib/libfrr.c:1216
>     #11 0x5577160e4d6d in main zebra/main.c:540
>     #12 0x7fcf70c29d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
>
> Indirect leak of 24 byte(s) in 1 object(s) allocated from:
>     #0 0x7fcf718b4a57 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:154
>     #1 0x7fcf7126f8dd in qcalloc lib/memory.c:105
>     #2 0x7fcf71244129 in listnode_new lib/linklist.c:71
>     #3 0x7fcf71244238 in listnode_add lib/linklist.c:92
>     #4 0x55771621d938 in pbr_iptable_alloc_intern zebra/zebra_pbr.c:1019
>     #5 0x7fcf71217d79 in hash_get lib/hash.c:147
>     #6 0x55771621dad3 in zebra_pbr_add_iptable zebra/zebra_pbr.c:1030
>     #7 0x55771614d00c in zread_iptable zebra/zapi_msg.c:4131
>     #8 0x55771614e586 in zserv_handle_commands zebra/zapi_msg.c:4424
>     #9 0x5577162dae2c in zserv_process_messages zebra/zserv.c:521
>     #10 0x7fcf7137798e in event_call lib/event.c:2011
>     #11 0x7fcf71242ff1 in frr_run lib/libfrr.c:1216
>     #12 0x5577160e4d6d in main zebra/main.c:540
>     #13 0x7fcf70c29d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

Fixes: f80ec7e3d6 ("zebra: handle iptable list of interfaces")
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>