tcpconns plugin: add support for AIX

tcpconns plugin: add support for AIX

Hi.

In AIX there is a undocumented function/syscall in libc: netinfo
returns a structure with the state of the tcp connections.

I didn't found the description or info abut this syscall,  I guess is
something like this:

int netinfo (int proto, void *data, int *size,  int n);

and the struct something like this: (with some work we can guess the
unknow remaining bytes)

struct netinfo_header {
        unsigned int proto;
        unsigned int size;
        struct netinfo_entry e[];
};
struct netinfo_entry {
        uint32_t unknow1;
        uint32_t unknow2;
        uint16_t dstport;
        uint16_t unknow3;
        struct in6_addr dstaddr;
        uint16_t srcport;
        uint16_t unknow4;
        struct in6_addr srcaddr;
        uint32_t unknow01[4];
        uint32_t unknow02[2];
        uint16_t so_options;
        uint16_t unknow02a;
        uint16_t so_q0len;
        uint16_t so_qlen;
        uint16_t so_qlimit;
        uint16_t so_dqlen;
        uint32_t unknow03[4];
        struct {
                uint32_t sb_hiwat;
                uint32_t unknow01;
                uint32_t unknow02;
                uint32_t unknow03;
                uint32_t sb_mbmax;
                uint32_t unknow04;
                uint32_t sb_lowat;
                uint16_t sb_flags;
                uint16_t unknow05;
        } rcvbuf;
        uint32_t unknow07;
        uint32_t unknow08[2];
        uint32_t unknow09;
        struct {
                uint32_t sb_hiwat;
                uint32_t unknow01;
                uint32_t unknow02;
                uint32_t unknow03;
                uint32_t sb_mbmax;
                uint32_t unknow04;
                uint32_t sb_lowat;
                uint16_t sb_flags;
                uint16_t unknow05;
        } sndbuf;
        uint32_t unknow11;
        uint32_t so_uid;
        uint16_t so_special;
        uint16_t so_special2;
        uint16_t tcp_state;
        uint16_t unknow12;
        uint32_t tcp_flags;
        uint32_t tcp_mss;
        uint32_t unknow15;
};

Signed-off-by: Florian Forster <octo@collectd.org>