Settable socket option requirements

A type X meets the SettableSocketOption requirements if it satisfies the requirements listed below.

In the table below, a denotes a (possibly const) value of type X, p denotes a (possibly const) value that meets the Protocol requirements, and u denotes an identifier.

Table 26. SettableSocketOption requirements for extensible implementations

expression	type	assertion/note pre/post-conditions
`a.level(p)`	`int`	Returns a value suitable for passing as the level argument to POSIX `setsockopt()` (or equivalent).
`a.name(p)`	`int`	Returns a value suitable for passing as the option_name argument to POSIX `setsockopt()` (or equivalent).
`a.data(p)`	`const void*`	Returns a pointer suitable for passing as the option_value argument to POSIX `setsockopt()` (or equivalent).
`a.size(p)`	`size_t`	Returns a value suitable for passing as the option_len argument to POSIX `setsockopt()` (or equivalent), after appropriate integer conversion has been performed.