pkg: provide sock_tcp support for lwip

Makefile.dep

pkg/lwip/Makefile.include

pkg/lwip/contrib/sock/lwip_sock.c

pkg/lwip/contrib/sock/tcp/Makefile

pkg/lwip/contrib/sock/tcp/lwip_sock_tcp.c

pkg/lwip/include/lwip/sock_internal.h

pkg/lwip/include/sock_types.h

tests/lwip_sock_tcp/Makefile

tests/lwip_sock_tcp/README.md

tests/lwip_sock_tcp/constants.h

tests/lwip_sock_tcp/main.c

tests/lwip_sock_tcp/stack.c

tests/lwip_sock_tcp/stack.h

tests/lwip_sock_tcp/tests/01-run.py