ipobfs_mod sets up 2 hooks : one for inbound, one for outbound

module takes parameters
 pre=<priority>		(default : mangle)
 prehook=<hooknum>	(default : prerouting)
 post=<priority>	(default : mangle)
 posthook=<hooknum>	(default : postrouting)

priority : mangle (default), raw, filter or <integer> 
 raw = NF_IP_PRI_RAW+1
 mangle = NF_IP_PRI_MANGLE+1
 filter = NF_IP_PRI_FILTER+1
 <integer> = positive or negative decimal or hex value. hex start with 0x prefix

hooknum : prerouting (inbound default), input, output, forward, postrouting (outbound default) or <integer>
 prerouting = NF_INET_PRE_ROUTING
 input = NF_INET_LOCAL_IN
 forward = NF_INET_FORWARD
 output = NF_INET_LOCAL_OUT
 postrouting = NF_INET_POST_ROUTING
 <integer> = decimal or hex value. hex start with 0x prefix

valid hooknum numbers :

enum nf_inet_hooks {
	NF_INET_PRE_ROUTING = 0,
	NF_INET_LOCAL_IN = 1,
	NF_INET_FORWARD = 2,
	NF_INET_LOCAL_OUT = 3,
	NF_INET_POST_ROUTING = 4
};

priorities :

enum nf_ip_hook_priorities {
	NF_IP_PRI_FIRST = INT_MIN,
	NF_IP_PRI_CONNTRACK_DEFRAG = -400,
	NF_IP_PRI_RAW = -300,
	NF_IP_PRI_SELINUX_FIRST = -225,
	NF_IP_PRI_CONNTRACK = -200,
	NF_IP_PRI_MANGLE = -150,
	NF_IP_PRI_NAT_DST = -100,
	NF_IP_PRI_FILTER = 0,
	NF_IP_PRI_SECURITY = 50,
	NF_IP_PRI_NAT_SRC = 100,
	NF_IP_PRI_SELINUX_LAST = 225,
	NF_IP_PRI_CONNTRACK_HELPER = 300,
	NF_IP_PRI_CONNTRACK_CONFIRM = INT_MAX,
	NF_IP_PRI_LAST = INT_MAX,
};