This patch reintroduces the LwIP stack to libc as a VFS plugin
implementing the socket_fs interface. Rather than use LwIP's socket
emulation layer this plugin interfaces directly to LwIP raw API and is
single threaded.
The internal TCP parameters of the stack are untuned.
Fix#2050Fix#2335
Rename LwIP library in preparation for removal of LwIP libc plugin. The
current LwIP library will be replaced with a new version stripped of its
synchronous socket support. The next version will be incompatible with
the current, so removing 'lwip.lib.so' completely for a period makes it
easy to identify legacy users.
Fix#2797
When calling 'connect()' in nonblocking mode and the connection has been
established, don't call 'tcp_connect()' again, which would trigger an
assertion with the message 'tcp_connect: can only connect from state
CLOSED'.
Fixes#2039
