Espressif patches in 2.1.3 esp on top of 2.1.3 rel

commit id	summary/ MR	Status
16f91b2b	FIX: arp: Return ERR_MEM on ARP queue full
358ee481	WIP: Temporarily add write-protect to api_msg	IDF-4857
86bf22d6	WIP: Temporarily break ipv6 zoning to pass IT_* tests	IDF-4856
d9131817	test/napt: Add unit test for IP forward with PBUF_REF	IDF-4797
c1a2a722	napt: Fix PBUF_REF type to clone the pbuf before forwarding	IDF-4800
768c2a4c	PPP: Add test exhibiting empty packet null-deref	IDF-4797
097b56c2	PPP: Fix null-deref when processing wrong packet	IDF-4847: P10013, P10179, B58817
ba29c9ac	dns: Add API to clear dns cache	IDF-4839
9f432e91	timeout: Add function for deinit system timers	IDF-4847: P10013, P10179, B58817
c28cb03d	sntp: Fix client receive KOD packet that make pool MEMP_SYS_TIMEOUT not be freed	IDF-4847: P10013, P10179, B58817
44755e73	dns: Fix server_idx increasing to DNS_MAX_SERVERS and trigger the LWIP_ASSERT	IDF-4839
39d9c264	tcp_in: Flag the pcb as closing if TCP_EVENT_CLOSED refused	IDF-4847: P10013, P10179, B58817
115c0e2d	dhcp: Add dhcp state debug info	IDF-4817: PR12, P10194
b0884121	slip: Fix SLIP RX linked list append.	IDF-4847: P10013, P10179, B58817
83633d81	tcp_in: Fix for potential segment overflow	IDF-4852
ea22e8f6	nd6: Queue IPv6 packets while ND6 inprogress	IDF-4849
d4839f6c	arp: Return ERR_MEM on ARP queue full	IDF-4849
6c65a09e	ip_frag: Drop IPv6 packets larger than MTU	IDF-4846
12bcb048	ppp: Fix potential array overflow	IDF-4847: P10013, P10179, B58817
02048871	sockets: Fix free-select-locked after udp close	IDF-4794
afb13b4d	ip_frag: Drop IPv4 packets larger than MTU	IDF-4846
ca4c7662	api_msg: Fixes for sock close from another thread	IDF-4794
95d63b3e	sockets: Fix potential race when socket is closed already	IDF-4794
8188897e	sockets: Fix select-waiter when socket closed abruptly	IDF-4794
e98e90cb	ipv6: Support IPv4/IPv6 mapped PCBs	IDF-4845
2b38d2c8	autoip: Make max-conflics and rate-limit configurable	IDF-4843
6a4b9f57	dns: Support for fallback DNS server	IDF-4839
33e3d3eb	igmp/mld6: Add on-demand timers config	IDF-4837
f978e87f	dhcp: Add hook for appending extra client's request options	IDF-4817: PR12, P10194
632ac61f	dhcp/test: Add dhcp option tests for platform hooks	IDF-4817: PR12, P10194
0633e7d1	dhcp: Continuously try to rebind in t2 (if failed in t1)	IDF-4817: PR12, P10194
729d724c	dhcp: Set hostname for DISCOVER packets	IDF-4817: PR12, P10194
73a92e31	dhcp: Enable custom config for timeouts, thresholds, delays	IDF-4817: PR12, P10194
14bba8e3	dhcp: Add post_init hook to allow skip discovery	IDF-4817: PR12, P10194
319d4d3c	napt: Add basic support for NAT by martin-ger	IDF-4800
bc507222	ipv6: Add error check on joining incorrect multicast address	IDF-4799
72105e53	tcp: Make retransmission timeout (RTO) configurable	IDF-4798: P10197
0a9dad95	api_msg: Support sock close from another thread	IDF-4794
5f246f5f	ci: Add unit test suite to validate tcp state transitions	IDF-4797
4a2fb780	ci: Add github/lab build/run unit tests on linux	IDF-4797
08f1b41d	ci: Update esp-lwip's version to 2.1.3-esp	IDF-4797
dd27077a	Fix compile error with GCC 8 in makefsdata	IDF-4797