mac80211: correct use of IEEE80211_VHT_CAP_RXSTBC_X

mac80211: correct use of IEEE80211_VHT_CAP_RXSTBC_X

BugLink: https://bugs.launchpad.net/bugs/1836426
[ Upstream commit 67d1ba8a6dc83d90cd58b89fa6cbf9ae35a0cf7f ]

The mod mask for VHT capabilities intends to say that you can override
the number of STBC receive streams, and it does, but only by accident.
The IEEE80211_VHT_CAP_RXSTBC_X aren't bits to be set, but values (albeit
left-shifted).  ORing the bits together gets the right answer, but we
should use the _MASK macro here instead.

Signed-off-by: Danek Duvall <duvall@comfychair.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>