selftests/net: Add TCP-AO ICMPs accept test

selftests/net: Add TCP-AO ICMPs accept test

Reverse to icmps-discard test: the server accepts ICMPs, using
TCP_AO_CMDF_ACCEPT_ICMP and it is expected to fail under ICMP
flood from client. Test that the default pre-TCP-AO behaviour functions
when TCP_AO_CMDF_ACCEPT_ICMP is set.

Expected output for ipv4 version (in case it receives ICMP_PROT_UNREACH):
> # ./icmps-accept_ipv4
> 1..3
> # 3209[lib/setup.c:166] rand seed 1642623870
> TAP version 13
> # 3209[lib/proc.c:207]    Snmp6             Ip6InReceives: 0 => 1
> # 3209[lib/proc.c:207]    Snmp6             Ip6InNoRoutes: 0 => 1
> # 3209[lib/proc.c:207]    Snmp6               Ip6InOctets: 0 => 76
> # 3209[lib/proc.c:207]    Snmp6            Ip6InNoECTPkts: 0 => 1
> # 3209[lib/proc.c:207]      Tcp                    InSegs: 3 => 23
> # 3209[lib/proc.c:207]      Tcp                   OutSegs: 2 => 22
> # 3209[lib/proc.c:207]  IcmpMsg                   InType3: 0 => 4
> # 3209[lib/proc.c:207]     Icmp                    InMsgs: 0 => 4
> # 3209[lib/proc.c:207]     Icmp            InDestUnreachs: 0 => 4
> # 3209[lib/proc.c:207]       Ip                InReceives: 3 => 27
> # 3209[lib/proc.c:207]       Ip                InDelivers: 3 => 27
> # 3209[lib/proc.c:207]       Ip               OutRequests: 2 => 22
> # 3209[lib/proc.c:207]    IpExt                  InOctets: 288 => 3420
> # 3209[lib/proc.c:207]    IpExt                 OutOctets: 124 => 3244
> # 3209[lib/proc.c:207]    IpExt               InNoECTPkts: 3 => 25
> # 3209[lib/proc.c:207]   TcpExt               TCPPureAcks: 1 => 2
> # 3209[lib/proc.c:207]   TcpExt           TCPOrigDataSent: 0 => 20
> # 3209[lib/proc.c:207]   TcpExt              TCPDelivered: 0 => 19
> # 3209[lib/proc.c:207]   TcpExt                 TCPAOGood: 3 => 23
> ok 1 InDestUnreachs delivered 4
> ok 2 server failed with -92: Protocol not available
> ok 3 TCPAODroppedIcmps counter didn't change: 0 >= 0
> # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0

Expected output for ipv6 version (in case it receives ADM_PROHIBITED):
> # ./icmps-accept_ipv6
> 1..3
> # 3277[lib/setup.c:166] rand seed 1642624035
> TAP version 13
> # 3277[lib/proc.c:207]    Snmp6             Ip6InReceives: 6 => 31
> # 3277[lib/proc.c:207]    Snmp6             Ip6InDelivers: 4 => 29
> # 3277[lib/proc.c:207]    Snmp6            Ip6OutRequests: 4 => 24
> # 3277[lib/proc.c:207]    Snmp6               Ip6InOctets: 592 => 4492
> # 3277[lib/proc.c:207]    Snmp6              Ip6OutOctets: 332 => 3852
> # 3277[lib/proc.c:207]    Snmp6            Ip6InNoECTPkts: 6 => 31
> # 3277[lib/proc.c:207]    Snmp6               Icmp6InMsgs: 1 => 6
> # 3277[lib/proc.c:207]    Snmp6       Icmp6InDestUnreachs: 0 => 5
> # 3277[lib/proc.c:207]    Snmp6              Icmp6InType1: 0 => 5
> # 3277[lib/proc.c:207]      Tcp                    InSegs: 3 => 23
> # 3277[lib/proc.c:207]      Tcp                   OutSegs: 2 => 22
> # 3277[lib/proc.c:207]   TcpExt               TCPPureAcks: 1 => 2
> # 3277[lib/proc.c:207]   TcpExt           TCPOrigDataSent: 0 => 20
> # 3277[lib/proc.c:207]   TcpExt              TCPDelivered: 0 => 19
> # 3277[lib/proc.c:207]   TcpExt                 TCPAOGood: 3 => 23
> ok 1 Icmp6InDestUnreachs delivered 5
> ok 2 server failed with -13: Permission denied
> ok 3 TCPAODroppedIcmps counter didn't change: 0 >= 0
> # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0

With some luck the server may fail with ECONNREFUSED (depending on what
icmp packet was delivered firstly).
For the kernel error handlers see: tab_unreach[] and icmp_err_convert[].

Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>