Only try to set MTU when it isn't correct
Only try to set MTU when it isn't correct

This allows fastd to run completely without root privileges when the TUN/TAP
device is pre-created

fpletz/fastd,fpletz/fastd,rlei/fastd-android,rlei/fastd-android,rlei/fastd-android,fpletz/fastd,rlei/fastd-android,rlei/fastd-android,fpletz/fastd,fpletz/fastd