MEDIUM: ssl: add 300s supported time skew on OCSP response update.

OCSP_MAX_RESPONSE_TIME_SKEW can be set to a different value at
compilation (default is 300 seconds).
diff --git a/include/common/defaults.h b/include/common/defaults.h
index 0d18281..c53db08 100644
--- a/include/common/defaults.h
+++ b/include/common/defaults.h
@@ -235,4 +235,7 @@
 #define OCSP_MAX_CERTID_ASN1_LENGTH 128
 #endif
 
+#ifndef OCSP_MAX_RESPONSE_TIME_SKEW
+#define OCSP_MAX_RESPONSE_TIME_SKEW 300
+#endif
 #endif /* _COMMON_DEFAULTS_H */