bond: Revalidate when lacp_negotiated status changes.

bond: Revalidate when lacp_negotiated status changes.

Typically, when the lacp_negotiated flag changes, the result of
bond_is_tcp_hash() will change as well.  However, for certain bond
types (SLB, Active-Backup, etc) this may not be true.  Since the
lacp_negotiated flag affects the results of
bond_check_admissibility() revalidation needs to happen whenever it
changes.  This patch makes the revalidation explicit.

Signed-off-by: Ethan Jackson <ethan@nicira.com>