This commit updates lxip from version 4.4.3 to 6.1.20. It uses the
current lx_kit approach and is a shared library again. The stack has
been tested for x86_32/x86_64/arm_v6/arm_v7/arm_8.
The C-interface of the IP stack can be found under
lxip/include/genode_c_api/socket.h.
issue #5104
