tests: avoid spurious warnings about gl_sockets_startup

tests: avoid spurious warnings about gl_sockets_startup

Fedora rawhide's gcc version 4.7.0 20120119 with -Wunused-value
would warn about every use of "gl_sockets_startup (SOCKETS_1_1);"
reporting a "statement with no effect".
* tests/test-accept.c (main): Mark as "(void)".
* tests/test-accept4.c (main): Likewise.
* tests/test-bind.c (main): Likewise.
* tests/test-connect.c (main): Likewise.
* tests/test-getpeername.c (main): Likewise.
* tests/test-getsockname.c (main): Likewise.
* tests/test-getsockopt.c (main): Likewise.
* tests/test-listen.c (main): Likewise.
* tests/test-recv.c (main): Likewise.
* tests/test-recvfrom.c (main): Likewise.
* tests/test-send.c (main): Likewise.
* tests/test-sendto.c (main): Likewise.
* tests/test-setsockopt.c (main): Likewise.
* tests/test-shutdown.c (main): Likewise.