[NETFILTER]: xt_sctp: fix mistake to pass a pointer where array is required

Macros like SCTP_CHUNKMAP_XXX(chukmap) require chukmap to be an array,
but match_packet() passes a pointer to these macros. Also remove the
ELEMCOUNT macro and fix a bug in SCTP_CHUNKMAP_COPY.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>