netsnmp: don't list openssl as a hard dependency

netsnmp can be compiled without ssl support, so don't list it as a hard
dependency and only compile in support if enabled by the user.

package/netsnmp/Config.in

@@ -1,6 +1,5 @@
 config BR2_PACKAGE_NETSNMP
 	bool "netsnmp"
-	select BR2_PACKAGE_OPENSSL
 	help
 	  Suite of applications used to implement SNMP v1, SNMP v2c, and
 	  SNMP v3 using both IPv4 and IPv6.

package/netsnmp/netsnmp.mk

@@ -130,7 +130,7 @@ endif
 	$(INSTALL) -D -m 0644 $(NETSNMP_DIR)/agent/mibgroup/header_complex.h $(STAGING_DIR)/usr/include/net-snmp/agent/header_complex.h
 	$(INSTALL) -D -m 0755 package/netsnmp/S59snmpd $(TARGET_DIR)/etc/init.d/S59snmpd
 
-netsnmp: openssl $(TARGET_DIR)/usr/sbin/snmpd
+netsnmp: $(if $(BR2_PACKAGE_OPENSSL),openssl) $(TARGET_DIR)/usr/sbin/snmpd
 
 netsnmp-headers: $(TARGET_DIR)/usr/include/net-snmp/net-snmp-config.h
 	$(INSTALL) -d $(TARGET_DIR)/usr/include/net-snmp