capabilities: make capability selection case insensitive.

Everything else to do with algorithm selection and properties is case
insensitive.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12450)

providers/common/capabilities.c

@@ -17,6 +17,7 @@
 #include "internal/nelem.h"
 #include "internal/tlsgroups.h"
 #include "prov/providercommon.h"
+#include "e_os.h"
 
 typedef struct tls_group_constants_st {
     unsigned int group_id;   /* Group ID */
@@ -177,7 +178,7 @@ static int tls_group_capability(OSSL_CALLBACK *cb, void *arg)
 int provider_get_capabilities(void *provctx, const char *capability,
                               OSSL_CALLBACK *cb, void *arg)
 {
-    if (strcmp(capability, "TLS-GROUP") == 0)
+    if (strcasecmp(capability, "TLS-GROUP") == 0)
         return tls_group_capability(cb, arg);
 
     /* We don't support this capability */