Get rid of vector socket functions
isc_socket_recvv, isc_socket_sendv, isc_socket_sendtov, isc_socket_sendtov2 are used only by httpd and dig, we can get rid of them and simplify socket code.
isc_socket_recvv, isc_socket_sendv, isc_socket_sendtov, isc_socket_sendtov2 are used only by httpd and dig, we can get rid of them and simplify socket code.