Improve input validation for parameters in ASCONF and ASCONF-ACK chunks

Thanks to Tolya Korniltsev for drawing my attention to this part of the
code by reporting an issue for the userland stack.

sys/netinet/sctp_asconf.c

@@ -723,7 +723,7 @@ sctp_handle_asconf(struct mbuf *m, unsigned int offset,
 			sctp_m_freem(m_ack);
 			return;
 		}
-		if (param_length <= sizeof(struct sctp_paramhdr)) {
+		if (param_length < sizeof(struct sctp_asconf_paramhdr)) {
 			SCTPDBG(SCTP_DEBUG_ASCONF1, "handle_asconf: param length (%u) too short\n", param_length);
 			sctp_m_freem(m_ack);
 			return;
@@ -1743,7 +1743,7 @@ sctp_handle_asconf_ack(struct mbuf *m, int offset,
 			sctp_asconf_ack_clear(stcb);
 			return;
 		}
-		if (param_length < sizeof(struct sctp_paramhdr)) {
+		if (param_length < sizeof(struct sctp_asconf_paramhdr)) {
 			sctp_asconf_ack_clear(stcb);
 			return;
 		}