bonding: Export skip slave logic to function

[ Upstream commit 119d48fd4298594beccf4f2ecd00627826ce2646 ]

As a preparation for following change that add array of
all slaves, extract code that skip slave to function.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Stable-dep-of: f8a65ab2f3ff ("bonding: fix link recovery in mode 2 when updelay is nonzero")
Signed-off-by: Sasha Levin <sashal@kernel.org>