[tinydtls] Makefile.include: fixed GNRC vs. posix_sockets

When WITH_RIOT_GNRC is set in CFLAGS, tinydtls will use a more
compact address representation based on ipv6_addr_t instead of
POSIX-style sockaddr_in6 to identify sessions (cf. struct session_t).

When posix_sockets are used (as in libcoap, e.g.), the POSIX
address representation should be selected automatically for
consistency. This change adds -DWITH_RIOT_GNRC to CFLAGS only
when the module posix_sockets is not selected.

pkg/tinydtls/Makefile.include

@@ -14,7 +14,7 @@ ifneq (,$(filter tinydtls,$(USEMODULE)))
   # Dependencies partially under control of the App's requirements
 
   # The configuration for socket overrides Sock
-  ifeq (,$(filter WITH_RIOT_SOCKETS,$(CFLAGS)))
+  ifeq (,$(filter posix_sockets,$(USEMODULE)))
     CFLAGS += -DWITH_RIOT_GNRC
   endif