[nrf fromtree] net: sockets_offload: Fix build error with NO_OPTIMIZATIONS

When CONFIG_NO_OPTIMIZATIONS the compiler will not inline
socket_offload_dns_is_enabled(), which means calls to
socket_offload* remain, and the linker will fail with

in function `zsock_getaddrinfo': undefined reference to
`socket_offload_getaddrinfo'
in function `zsock_freeaddrinfo': undefined reference to
`socket_offload_freeaddrinfo'

Instead of relaying on that function being inlined and the
if'ed code being removed, let's just use the preprocessor.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>
(cherry picked from commit dc24583858b68c1119d99e03c410db53a8b04335)
Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

Author: aescolar

include/zephyr/net/socket_offload.h

@@ -67,10 +67,7 @@ void socket_offload_dns_enable(bool enable);
 #if defined(CONFIG_NET_SOCKETS_OFFLOAD)
 bool socket_offload_dns_is_enabled(void);
 #else
-static inline bool socket_offload_dns_is_enabled(void)
-{
-	return false;
-}
+#define socket_offload_dns_is_enabled() false
 #endif /* defined(CONFIG_NET_SOCKETS_OFFLOAD) */