Fix TSNs.

gtests/net/packetdrill/tests/bsd/sctp/sctp_icmp_passive.pkt

@@ -2,7 +2,7 @@
 // Check the handshake with en empty(!) cookie
 +0.0 bind(3, ..., ...) = 0
 +0.0 listen(3, 1) = 0
-+0.0 < sctp: INIT[tag=1 a_rwnd=4500 os=1 is=1 tsn=0]
++0.0 < sctp: INIT[tag=1 a_rwnd=4500 os=1 is=1 tsn=1]
 +0.0 > sctp: INIT_ACK[tag=2 tsn=0] // faked cookie
 +0.1 < sctp: COOKIE_ECHO[]
 +0.0 > sctp: COOKIE_ACK[]
@@ -17,6 +17,6 @@
 +0.1 < sctp: SACK[tsn=1 a_rwnd=4500 gaps=[] dups=[]]
 // Tear down the association
 +0.0 close(4) = 0
-+0.0 > sctp: SHUTDOWN[tsn=2]
++0.0 > sctp: SHUTDOWN[tsn=0]
 +0.1 < sctp: SHUTDOWN_ACK[]
 +0.0 > sctp: SHUTDOWN_COMPLETE[]