Some HP laptops have only a single wifi antenna. This would not be a
problem except that they were shipped with an incorrectly encoded
EFUSE. It should have been possible to open the computer and transfer
the antenna connection to the other terminal except that such action
might void the warranty, and moving the antenna broke the Windows
driver. The fix was to add a module option that would override the
EFUSE encoding. That was done with commit c18d8f50 ("rtlwifi:
rtl8723be: Add antenna select module parameter"). There was still a
problem with Bluetooth coexistence, which was addressed with commit
baa17022 ("rtlwifi: btcoexist: Implement antenna selection").
There were still problems, thus there were commit 0ff78ade
("rtlwifi: rtl8723be: fix ant_sel code") and commit 6d622692
("rtlwifi: btcoexist: Fix antenna selection code"). Despite all these
attempts at fixing the problem, the code is not yet right. A proper
fix is important as there are now instances of laptops having
RTL8723DE chips with the same problem.

The module parameter ant_sel is used to control antenna number and path.
At present enum ANT_{X2,X1} is used to define the antenna number, but
this choice is not intuitive, thus change to a new enum ANT_{MAIN,AUX}
to make it more readable. This change showed examples where incorrect
values were used. It was also possible to remove a workaround in
halbtcoutsrc.c.

The experimental results with single antenna connected to specific path
are now as follows:
  ant_sel  ANT_MAIN(#1)  ANT_AUX(#2)
     0        -8            -62
     1        -62           -10
     2        -6            -60
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Fixes: c18d8f50 ("rtlwifi: rtl8723be: Add antenna select module parameter")
Fixes: baa17022 ("rtlwifi: btcoexist: Implement antenna selection")
Fixes: 0ff78ade ("rtlwifi: rtl8723be: fix ant_sel code")
Fixes: 6d622692 ("rtlwifi: btcoexist: Fix antenna selection code")
Cc: Stable <stable@vger.kernel.org> # 4.7+
Reviewed-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>