[NETFILTER]: H.323 helper: move some function prototypes to ip_conntrack_h323.h

Move prototypes of NAT callbacks to ip_conntrack_h323.h. Because the
use of typedefs as arguments, some header files need to be moved as
well.

Signed-off-by: Jing Min Zhao <zhaojingmin@users.sourceforge.net>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>