if_lagg is now using non-sleepable rmlocks to protect its internal state. In many cases it calls if_ioctl() interface method while still holding the lock. According to my conversation with glebius@ that is not correct, since if_ioctl() should be allowed to sleep. This patch introduces another sx lock to protect code paths that require sleeping, while still uses old rmlock to protect hot non-sleepable data paths.

This change allows to remove taskqueue decoupling used before to change interface addresses without holding the lock. Instead the new code uses sx lock to protect direct if_ioctl() calls.

As another bonus, the new code synchronizes enabled capabilities of member interfaces, and allows to control them with ifconfig laggX, that was impossible before. This part should fix inter-operation with if_bridge, that may need to disable some capabilities, such as TXCSUM or LRO, to allow bridging with non-capable interfaces.