staging: rtl8188eu: don't duplicate ieee80211 WLAN_CAPABILITY_* constants

linux/ieee80211.h already defines constants for capability bits.
Include it where needed, resolve discrepancies in naming, and remove the
duplicated definitions.

Also, make use of WLAN_CAPABILITY_IS_STA_BSS() macro to check if neither
ESS nor IBSS capability bits are set.

Signed-off-by: Jakub Sitnicki <jsitnicki@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>