My vm is x86 architecture:
# uname -m 
x86pc
and my lsm library has the same permissions as lsm-pf-v4.so does:
# ls -l /lib/dll/lsm-libfilter.so 
-rwxrwxr-x   1 root      root           7384 Feb 13 14:43 /lib/dll/lsm-libfilter.so
# ls -l /lib/dll/lsm-pf-v4.so      
-rwxrwxr-x   1 root      root         239208 Feb 28  2017 /lib/dll/lsm-pf-v4.so

my code:
#include <sys/types.h>
#include <errno.h>
#include <sys/param.h>
#include <sys/conf.h>
#include <sys/socket.h>
#include <sys/mbuf.h>
#include <net/if.h>
#include <net/pfil.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/slog.h>
#include <sys/slogcodes.h>
#include "sys/io-pkt.h"
#include "nw_datastruct.h"


static int input_hook(void *arg, struct mbuf **m,
                      struct ifnet *ifp, int dir, int fib)
{
    slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
                      _SLOG_ERROR, "input");
    return 0;
}

static int output_hook(void *arg, struct mbuf **m,
                       struct ifnet *ifp, int dir, int fib)
{
    slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
                      _SLOG_ERROR, "output");
    return 0;
}


static int deinit_module(void);
static int iface_hook(void *arg, struct mbuf **m,
                      struct ifnet *ifp, int dir, int fib)
{
	slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
	                  _SLOG_ERROR,"Iface hook called ... ");
    if (m == (struct mbuf **)PFIL_IFNET_ATTACH) {
    	slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
    	                  _SLOG_ERROR,"Interface attached\n");
    } else if (m == (struct mbuf **)PFIL_IFNET_DETACH) {
    	slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
    	                  _SLOG_ERROR,"Interface detached\n");
        deinit_module();
    }
    return 0;
}

static int ifacecfg_hook(void *arg, struct mbuf **m,
                         struct ifnet *ifp, int dir, int fib)
{

	slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
	                  _SLOG_ERROR,"Iface cfg hook called with 0x%p\n", m);

    return 0;
}

static int deinit_module(void)
{
    struct pfil_head *pfh_inet;
    pfh_inet = pfil_head_get(PFIL_TYPE_AF, AF_INET);
    if (pfh_inet == NULL) {
        return ESRCH;
    }
    pfil_remove_hook(input_hook, NULL, PFIL_IN | PFIL_WAITOK,
                     pfh_inet);
    pfil_remove_hook(output_hook, NULL, PFIL_OUT | PFIL_WAITOK,
                     pfh_inet);
    pfh_inet = pfil_head_get(PFIL_TYPE_IFNET, 0);
        if (pfh_inet == NULL) {
            return ESRCH;
        }

    pfil_remove_hook(ifacecfg_hook, NULL, PFIL_IFNET, pfh_inet);

    pfil_remove_hook(iface_hook, NULL, PFIL_IFNET | PFIL_WAITOK,
                         pfh_inet);
    slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
                  _SLOG_ERROR,
				  "Unloaded pfil hook\n");

    return 0;
}

int pfil_entry(void *dll_hdl, struct _iopkt_self *iopkt,
               char *options)
{
	printf("pfil_entry+++++++++ enter\n");
    struct pfil_head *pfh_inet;
    pfh_inet = pfil_head_get(PFIL_TYPE_AF, AF_INET);
    if (pfh_inet == NULL) {
        return ESRCH;
    }
    pfil_add_hook(input_hook, NULL, PFIL_IN | PFIL_WAITOK,
                  pfh_inet);
    pfil_add_hook(output_hook, NULL, PFIL_OUT | PFIL_WAITOK,
                  pfh_inet);

    pfh_inet = pfil_head_get(PFIL_TYPE_IFNET,0);
        if (pfh_inet == NULL) {
            return ESRCH;
        }

    pfil_add_hook(iface_hook, NULL, PFIL_IFNET, pfh_inet);
    pfil_add_hook(ifacecfg_hook, NULL, PFIL_IFADDR, pfh_inet);

    slogf(_SLOG_SETCODE(_SLOGC_TEST, 2),
                      _SLOG_ERROR, "Loaded pfil hook\n");

    return 0;
}

struct _iopkt_lsm_entry IOPKT_LSM_ENTRY_SYM(pfil) =
  IOPKT_LSM_ENTRY_SYM_INIT(pfil_entry);


and Makefile:
ARTIFACT = libfilter_1.so

#Build architecture/variant string, possible...