Don't put dhclient into a loop when interface-mtu is present
in a lease.
dhclient.c r1.634 made every RTM_IFINFO restart the DHCP protocol
and obtain a new/renewed lease. If the lease contained
interface-mtu the interface MTU was set. An RTM_IFINFO is
generated every time an interface MTU is set.
So only set the interface MTU if it is different from the
existing MTU. Fix using %d to print an unsigned value in passing.
Noticed and fix inmproved & tested by Bj??rn Ketelaars while
usihg the wifi on Dutch Railways.
UnifiedSplitRaw