Merge pull request #10059 from miri64/pkg/enh/lwIP-2.1

Makefile.dep

makefiles/pseudomodules.inc.mk

pkg/lwip/Makefile

pkg/lwip/Makefile.include

pkg/lwip/contrib/netdev/lwip_netdev.c

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

pkg/lwip/contrib/sock/lwip_sock.c

pkg/lwip/patches/0001-Fix-warnings.patch

...es/0001-lowpan6.c-Fix-IEEE-802.15.4-address-setting.patch

pkg/lwip/patches/0002-Add-RIOT-Makefiles.patch

tests/lwip_sock_ip/stack.c

tests/lwip_sock_tcp/Makefile

tests/lwip_sock_udp/stack.c