net: sfp: rename sfp_sm_ins_next() as sfp_sm_mod_next()

sfp_sm_ins_next() modifies the module state machine.  Change it's name
to reflect this.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>