In XNS5, and subsequently in POSIX-2001 it was changed to socklen_t.
To accomodate for this while preserving binary compatibility with the
old interface, prepend or append 32 bits of padding, depending on
the (LP64 data model) architecture's endianness. Fixes PR
standards/21411 from Ben Harris.
This should be deleted the next time the libc major number is
incremented.
Also, update getnetbyaddr(3)'s `net' argument accordingly.
8d54bc1847