obj: fix memleak in parser_bison.y

obj: fix memleak in parser_bison.y

Each object (secmark, synproxy, quota, limit, counter) is dynamically allocated
by the parser and not freed at exit.
However, there is no need to use dynamic allocation here because struct obj
already provides the required storage. Update the grammar to ensure that
obj_alloc() is called before config occurs.

This fixes the following memleak (secmark as example):

 # valgrind --leak-check=full nft add secmark inet raw ssh \"system_u:object_r:ssh_server_packet_t:s0\"
 ==14643== Memcheck, a memory error detector
 ==14643== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
 ==14643== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
 ==14643== Command: nft add secmark inet raw ssh "system_u:object_r:ssh_server_packet_t:s0"
 ==14643==
 ==14643==
 ==14643== HEAP SUMMARY:
 ==14643==     in use at exit: 256 bytes in 1 blocks
 ==14643==   total heap usage: 41 allocs, 40 frees, 207,809 bytes allocated
 ==14643==
 ==14643== 256 bytes in 1 blocks are definitely lost in loss record 1 of 1
 ==14643==    at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
 ==14643==    by 0x4E72074: xmalloc (utils.c:36)
 ==14643==    by 0x4E72074: xzalloc (utils.c:65)
 ==14643==    by 0x4E89A31: nft_parse (parser_bison.y:3706)
 ==14643==    by 0x4E778E7: nft_parse_bison_buffer (libnftables.c:375)
 ==14643==    by 0x4E778E7: nft_run_cmd_from_buffer (libnftables.c:443)
 ==14643==    by 0x40170F: main (main.c:326)

Fixes: f44ab88b1088e ("src: add synproxy stateful object support")
Fixes: 3bc84e5c1fdd1 ("src: add support for setting secmark")
Fixes: c0697eabe832d ("src: add stateful object support for limit")
Fixes: 4d38878b39be4 ("src: add/create/delete stateful objects")
Signed-off-by: Eric Jallot <ejallot@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>