rtwn: remove SEQ_SEL, replace with a QOS bit

I've reviewed all of the linux vendor and upstream drivers.
This SEQ_SEL field isn't a mask and doesn't ever look like it
it was; instead this bit is set to tag QoS data frames.

In fact, it effectively was set to 0 for STA frames and potentially 1
for broadcast/multicast frames as the STA macid of 0 and broadcast/
multicast macid of 1 maps to that. In AP modes it would be tagged
based on bit 0.

So, bring it in line with the vendor and linux drivers.

Locally tested:

• RTL8192CU, STA, hostap
• RTL8188EU, STA
• RTL8192EU, STA

Differential Revision: https://reviews.freebsd.org/D48092