rtlwifi_new: Fix all drivers to build correctly on Ubuntu 3.13

In kernel 3.13.0-XX where XX is >= 32, Ubuntu has implemented the API
change that was introduced in mainline V3.15 by commit d8ca16db6bb2 ("mac80211:
add length check in ieee80211_is_robust_mgmt_frame()"). The result is that the
code in this repo gets it wrong for Ubuntu kernels. The result is
a kernel that crashes when using the corresponging driver. Thanks to user
"lenonk" at GitHub, there is a fix. I have not tested it as I do not use one
of the affected kernels; however, it looks correct.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
rtlwifi_new: Modify Makefile to save drivers before installing new ones

Whe uninstalling the drivers, the saved versions are restored. Firmware is
not touched when uninstalling.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>