Upgrade LWIP to 2.2.1

(STABLE-2.2.1):  ++ New features:  2023-10-11: Faidon Liambotis

  * Add MEM_CUSTOM_ALLOCATOR and make LIBC a subset of it  2023-09-29: Jiri Findejs

  * mqtt: support binary Will Message  ++ Bugfixes:  2024-02-19: Simon Goldschmidt

  * tcpip: fix that TCPIP_CORE_LOCK is not released for LWIP_TIMERS==0  2024-01-09: Simon Goldschmidt

  * snmp v3, ppp: prevent possible timing attacks by using a constant-runtime-memcmp when

    checking credentials  2023-01-04: Simon Goldschmidt

  * makefsdata: update tinydir.h to newest version (1.2.6)  2023-10-12: Borys Szefler

  * dhcp: fix memory corruption when LWIP_DHCP_MAX_DNS_SERVERS  > DNS_MAX_SERVERS  2023-10-11: Mazakazu

  * sockets: fix socket leak when using setsockopt/getsockopt hook with LWIP_NETCONN_FULLDUPLEX==1  2023-10-10: Simon Goldschmidt

  * sockets: fix bug #63898: allow socket option IPV6_CHECKSUM for both IPPROTO_IPV6 and IPPROTO_RAW  2023-10-10: Simon Goldschmidt

  * ipv6: fix ip6_current_header() after reassembly  2023-10-07: Simon Goldschmidt

  * ipv6 reassembly: fix detecting holes in reassembled packets  2023-10-04: Simon Goldschmidt

  * apps: http client: improve the HTTP client; ensure connection settings are passed  2023-10-03: Simon Goldschmidt

  * ipv6: frag: fix bogus icmp6 response on reassembly timeout  2023-09-28: Szabolcs Szekelyi

  * httpd: ensure headers are parsed case-insensitive  2023-09-28: Erik Ekman

  * Fix ND6 Router Advertisement parsing when NETIF_MAX_HWADDR_LEN is above 6.  2023-09-27: Hardy Griech

  * Fix iperf byte counting mode