Fixes

Along my work at Google Summer of Code I have found and fixed several bugs in nftables and libnftnl. Here is a list of these commits:

nftables

• parser: cap comment length to 128 bytes
• parser: Consolidate comment production

libnftnl

• expr: cmp: Use cmp2str() instead of directly access to array
• utils: Fix out of bound access in nftnl_family2str
• tests: masq: Fix wrong expression creation
• tests: Fix tests for immediate and lookup expressions
• expr: Fix lookup builder
• src: Fix nftnl_*_get_data() to return the real attribute length
• src: Fix missing nul-termination in nftnl_*_set_str()
• src: fix missing error checking in parser functions
• chain: Check correct attribute
• src: Fix leak in nftnl_*_unset()
• src: fix memory leaks at nft_[object]_nlmsg_parse