nf_conntrack.h: fix up fallout from implicit moduleparam.h presence

The implicit presence of module.h everywhere meant that this header
also was getting moduleparam.h which defines struct kernel_param.

Since it only needs to know that kernel_param is a struct, call that
out instead of adding an include of moduleparam.h -- to get rid of this:

include/net/netfilter/nf_conntrack.h:316: warning: 'struct kernel_param' declared inside parameter list
include/net/netfilter/nf_conntrack.h:316: warning: its scope is only this definition or declaration, which is probably not what you want

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>