Fix gcc 12 warnings about narrowing conversions of socket ioctl constants
when used as case labels, e.g:
> ../../../../src/winsup/cygwin/net.cc: In function ‘int get_ifconf(ifconf*, int)’:
> ../../../../src/winsup/cygwin/net.cc:1940:18: error: narrowing conversion of ‘2152756069’ from ‘long int’ to ‘int’ [-Wnarrowing]
Signed-off-by: Jon Turney <jon.turney@dronecode.org.uk>