Removed annoying check on netinet/ip.h for OpenBSD

I prefer to remove the check rather than to add the solution used
by Wine as we don't care about the associated define:

AC_CHECK_HEADERS([ \
    ...
    netinet/ip.h \
    netinet/tcp.h \
    ...
],,,[
    #ifdef HAVE_NETINET_IP_H
    # include <netinet/ip.h>
    #endif
])

configure.ac

@@ -65,10 +65,24 @@ AC_PROG_LIBTOOL
 AC_PROG_MAKE_SET
 AC_DISABLE_STATIC
 AC_PROG_LIBTOOL
+AC_CHECK_HEADERS([ \
+    termios.h \
+    sys/time.h \
+    unistd.h \
+    errno.h \
+    limits.h \
+    fcntl.h \
+    sys/types.h \
+    sys/socket.h \
+    sys/ioctl.h \
+    netinet/in.h \
+    netinet/tcp.h \
+    arpa/inet.h \
+])
 
 # Checks for header files.
 AC_HEADER_STDC
-AC_CHECK_HEADERS([termios.h sys/time.h unistd.h errno.h limits.h fcntl.h sys/types.h sys/socket.h sys/ioctl.h netinet/in.h netinet/ip.h netinet/tcp.h arpa/inet.h])
+
 
 # Checks for typedefs, structures, and compiler characteristics.
 AC_C_CONST