5.3.7 Martian Address Filtering
An IP source address is invalid if it is a special IP address, as
defined in 18.104.22.168 or 5.3.7, or is not a unicast address.
Only unicast adresses are allowed for source address. 255.255.255.255 is not a unicast address then it's considered invalid. Linux follows the standard.
Probably it's your wireless router that does strange things. What router is this?
Do you only have 1 ethernet adapter?
You can switch off these warnings with one of these:
net.ipv4.conf.all.log_martians = 0
net.ipv4.conf.default.log_martians = 0
net.ipv4.conf.lo.log_martians = 0
net.ipv4.conf.eth0.log_martians = 0
net.ipv4.conf.eth1.log_martians = 0
net.ipv4.conf.eth2.log_martians = 0
net.ipv4.conf.irda0.log_martians = 0
See your kernel documentation