[NETLINK]: Use nlmsg_trim() where appropriate

include/net/netlink.h

net/core/wireless.c

net/decnet/dn_route.c

net/decnet/dn_table.c

net/ipv4/inet_diag.c

net/ipv4/ipmr.c

net/netfilter/nf_conntrack_netlink.c

net/sched/act_api.c

net/sched/act_gact.c

net/sched/act_ipt.c

net/sched/act_mirred.c

net/sched/act_pedit.c

net/sched/act_police.c

net/sched/act_simple.c

net/sched/cls_api.c

net/sched/cls_basic.c

net/sched/cls_fw.c

net/sched/cls_route.c

net/sched/cls_rsvp.c

net/sched/cls_rsvp.h