flowtable: fix memleak in exit path

flowtable: fix memleak in exit path

Add missing loop in table_free().
Free all objects in flowtable_free() and add conditions in case of error recovery
in the parser (See commit 4be0a3f922a29).

Also, fix memleak in the parser.

This fixes the following memleak:

 # valgrind --leak-check=full nft add flowtable inet raw f '{ hook ingress priority filter; devices = { eth0 }; }'
 ==15414== Memcheck, a memory error detector
 ==15414== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
 ==15414== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
 ==15414== Command: nft add flowtable inet raw f {\ hook\ ingress\ priority\ filter;\ devices\ =\ {\ eth0\ };\ }
 ==15414==
 ==15414==
 ==15414== HEAP SUMMARY:
 ==15414==     in use at exit: 266 bytes in 4 blocks
 ==15414==   total heap usage: 55 allocs, 51 frees, 208,105 bytes allocated
 ==15414==
 ==15414== 5 bytes in 1 blocks are definitely lost in loss record 2 of 4
 ==15414==    at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
 ==15414==    by 0x5C64AA9: strdup (strdup.c:42)
 ==15414==    by 0x4E705ED: xstrdup (utils.c:75)
 ==15414==    by 0x4E93F01: nft_lex (scanner.l:648)
 ==15414==    by 0x4E85C1C: nft_parse (parser_bison.c:5577)
 ==15414==    by 0x4E75A07: nft_parse_bison_buffer (libnftables.c:375)
 ==15414==    by 0x4E75A07: nft_run_cmd_from_buffer (libnftables.c:443)
 ==15414==    by 0x40170F: main (main.c:326)
 ==15414==
 ==15414== 261 (128 direct, 133 indirect) bytes in 1 blocks are definitely lost in loss record 4 of 4
 ==15414==    at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
 ==15414==    by 0x4E705AD: xmalloc (utils.c:36)
 ==15414==    by 0x4E705AD: xzalloc (utils.c:65)
 ==15414==    by 0x4E560B6: expr_alloc (expression.c:45)
 ==15414==    by 0x4E56288: symbol_expr_alloc (expression.c:286)
 ==15414==    by 0x4E8A601: nft_parse (parser_bison.y:1842)
 ==15414==    by 0x4E75A07: nft_parse_bison_buffer (libnftables.c:375)
 ==15414==    by 0x4E75A07: nft_run_cmd_from_buffer (libnftables.c:443)
 ==15414==    by 0x40170F: main (main.c:326)

Fixes: 92911b362e906 ("src: add support to add flowtables")
Signed-off-by: Eric Jallot <ejallot@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>