fix compile warnings:
network-mysqld-packet.c: In function ‘network_mysqld_proto_get_fielddefs’:
network-mysqld-packet.c:685: warning: passing argument 2 of ‘network_mysqld_proto_get_int16’ from incompatible pointer type
network-mysqld-packet.c:686: warning: passing argument 2 of ‘network_mysqld_proto_get_int32’ from incompatible pointer type
network-mysqld-packet.c:687: warning: passing argument 2 of ‘network_mysqld_proto_get_int8’ from incompatible pointer type
network-mysqld-packet.c:688: warning: passing argument 2 of ‘network_mysqld_proto_get_int16’ from incompatible pointer type
network-mysqld-packet.c:689: warning: passing argument 2 of ‘network_mysqld_proto_get_int8’ from incompatible pointer type
network-mysqld-packet.c:701: warning: passing argument 2 of ‘network_mysqld_proto_get_int24’ from incompatible pointer type
network-mysqld-packet.c:704: warning: passing argument 2 of ‘network_mysqld_proto_get_int8’ from incompatible pointer type
network-mysqld-packet.c:707: warning: passing argument 2 of ‘network_mysqld_proto_get_int16’ from incompatible pointer type
network-mysqld-packet.c:708: warning: passing argument 2 of ‘network_mysqld_proto_get_int8’ from incompatible pointer type
network-mysqld-packet.c:712: warning: passing argument 2 of ‘network_mysqld_proto_get_int8’ from incompatible pointer type