sctp: remove redundant check when walking through a list of TLV parameters

When  pos.v <= (void *)chunk + end - ntohs(pos.p->length) and
ntohs(pos.p->length) >= sizeof(sctp_paramhdr_t) these two expressions are all true,
pos.v <= (void *)chunk + end - sizeof(sctp_paramhdr_t) *must* be true.

This patch removes this kind of redundant check.
It's same to  _sctp_walk_errors macro.

Signed-off-by: Shan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>