net: phy: simplify phy_mac_interrupt and related functions

When using phy_mac_interrupt() the irq number is set to
PHY_IGNORE_INTERRUPT, therefore phy_interrupt_is_valid() returns false.
As a result phy_change() effectively just calls phy_trigger_machine()
when called from phy_mac_interrupt() via phy_change_work(). So we can
call phy_trigger_machine() from phy_mac_interrupt() directly and
remove some now unneeded code.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>