Sets the socket option requested. Returns
undef on error.
Use integer constants provided by the
LEVEL and OPNAME. Values for LEVEL can also be obtained from
getprotobyname. OPTVAL might either be a packed string or an integer.
An integer OPTVAL is shorthand for pack("i", OPTVAL).
An example disabling Nagle's algorithm on a socket:
Portability issues: setsockopt in perlport.