batman-adv: Make NC capability changes atomic

commit 4635469f upstream.

Bitwise OR/AND assignments in C aren't guaranteed to be atomic. One
OGM handler might undo the set/clear of a specific bit from another
handler run in between.

Fix this by using the atomic set_bit()/clear_bit()/test_bit() functions.

Fixes: 3f4841ff ("batman-adv: tvlv - add network coding container")
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>