Revert "samples: sockets: Don't open the socket if the test protocol is enabled"

This reverts commit da0f3311ff1dddca06c42220bd51857fb3b4080a. It was
clearly intended to be a debugging aid when developing TCP2, not
intended for mainline. This fixes building this sample on POSIX
systems with Makefile.posix.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>