selftest: packetdrill: Import opt34/icmp-before-accept.pkt.

selftest: packetdrill: Import opt34/icmp-before-accept.pkt.

This imports the non-experimental version of icmp-before-accept.pkt.

This file tests the scenario where an ICMP unreachable packet for a
not-yet-accept()ed socket changes its state to TCP_CLOSE, but the
SYN data must be read without error, and the following read() returns
EHOSTUNREACH.

Note that this test support only IPv4 as icmp is used.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250927213022.1850048-9-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>