pkg: provide sock_ip support for lwip

Makefile.dep

pkg/lwip/Makefile.include

pkg/lwip/contrib/sock/Makefile

pkg/lwip/contrib/sock/ip/Makefile

pkg/lwip/contrib/sock/ip/lwip_sock_ip.c

pkg/lwip/contrib/sock/lwip_sock.c

pkg/lwip/include/lwip/sock_internal.h

pkg/lwip/include/lwipopts.h

pkg/lwip/include/sock_types.h

tests/lwip_sock_ip/Makefile

tests/lwip_sock_ip/README.md

tests/lwip_sock_ip/constants.h

tests/lwip_sock_ip/main.c

tests/lwip_sock_ip/stack.c

tests/lwip_sock_ip/stack.h

tests/lwip_sock_ip/tests/01-run.py