udp_ioctl() handles the following ioctl requests for udp file descriptors:
NWIOSUDPOPT: Set UDP OPTions. udp_ioctl() calls udp_setopt(), which gets data (specifically, a nwio_udpopt_t struct) from the user process and sets the options accordingly. Before a udp file descriptor can be used, the file descriptor must be configured by udp_ioctl().
NWIOGUDPOPT: Get UDP OPTions. Sends a nwio_udpopt_t struct to the process that opened the udp file descriptor which contains the configuration data for the udp file descriptor.
udp_ioctl() is called (indirectly) by sr_rwio().