Soft-deprecate obscure feature on property getters returning pointers

moc actually generates the right code for getters returning a pointer
to the type in question, or a reference to the type (a reference, one
would assume, does not require code changes). However, the same
extension is not valid for the setter: it can't receive the new value
by pointer.

Therefore, let's soft-deprecate the feature by removing its existence
from the documentation.

Task-number: QTBUG-33091
Change-Id: I27844213e051ec7fafeb4744089a0653aea6f1f3
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Update Linux interface getting to make fewer syscalls

Each time we call if_nametoindex, if_indextoname or somesuch, the libc
needs to open a socket, make an ioctl, and close the socket. Since we've
got most of the information we need anyway in the data from
getifaddrs(3), let's just use it

Change-Id: I572c212a27c4b9ffe57980b36f75bb04e6d5cf29
Reviewed-by: Jonas Gastal <gastal@intel.com>
Reviewed-by: Richard J. Moore <rich@kde.org>