nfct: remove unneeded included header

This fixes a compilation breakage when libnetfilter_cttimeout.h is
not installed.

Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
nfct: timeout: add support for default protocol timeout tuning

This new interface supersedes the /proc interface:

/proc/sys/net/netfilter/nf_conntrack_PROTO_STATE_timeout

to tune default conntrack timeout helpers.

 # nfct timeout default-get inet tcp
         .l3proto = 2,
         .l4proto = 6,
         .policy = {
                 .SYN_SENT = 120,
                 .SYN_RECV = 60,
                 .ESTABLISHED = 432000,
                 .FIN_WAIT = 120,
                 .CLOSE_WAIT = 60,
                 .LAST_ACK = 30,
                 .TIME_WAIT = 120,
                 .CLOSE = 10,
                 .SYN_SENT2 = 120,
                 .RETRANS = 300,
                 .UNACKNOWLEDGED = 300,
         },
 };

 # nfct timeout default-set inet tcp ESTABLISHED 100

As replacement for the existing /proc interfaces for timeout tweaking.
This feature requires a Linux kernel >= 3.13.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>