eap: Reset errno before calling strtoul() to parse EAP type

Reset errno to 0 before calling strtoul() since it sets errno only on
error cases. So the following test fails even on correct conversions if
errno had a value != 0.

Fixes #2506.

src/libstrongswan/eap/eap.c

@@ -157,6 +157,7 @@ eap_vendor_type_t *eap_vendor_type_from_string(char *str)
 			type = eap_type_from_string(part);
 			if (!type)
 			{
+				errno = 0;
 				type = strtoul(part, &end, 0);
 				if (*end != '\0' || errno)
 				{
@@ -166,6 +167,7 @@ eap_vendor_type_t *eap_vendor_type_from_string(char *str)
 			}
 			continue;
 		}
+		errno = 0;
 		vendor = strtoul(part, &end, 0);
 		if (*end != '\0' || errno)
 		{