Fix #70461: disable md5 code when it is not supported in net-snmp

Patch contributed by Alexander Bergmann.

Closes phpGH-6389.

Author: cmb69

NEWS

@@ -25,6 +25,10 @@ PHP                                                                        NEWS
 - ODBC:
   . Fixed bug #44618 (Fetching may rely on uninitialized data). (cmb)
 
+- SNMP:
+  . Fixed bug #70461 (disable md5 code when it is not supported in net-snmp).
+    (Alexander Bergmann, cmb)
+
 29 Oct 2020, PHP 7.3.24
 
 - Core:

ext/snmp/snmp.c

@@ -1208,10 +1208,13 @@ static int netsnmp_session_set_sec_level(struct snmp_session *s, char *level)
    Set the authentication protocol in the snmpv3 session */
 static int netsnmp_session_set_auth_protocol(struct snmp_session *s, char *prot)
 {
+#ifndef DISABLE_MD5
 	if (!strcasecmp(prot, "MD5")) {
 		s->securityAuthProto = usmHMACMD5AuthProtocol;
 		s->securityAuthProtoLen = USM_AUTH_PROTO_MD5_LEN;
-	} else if (!strcasecmp(prot, "SHA")) {
+	} else
+#endif
+	if (!strcasecmp(prot, "SHA")) {
 		s->securityAuthProto = usmHMACSHA1AuthProtocol;
 		s->securityAuthProtoLen = USM_AUTH_PROTO_SHA_LEN;
 	} else {