[IPV4]: [2/4] signed vs unsigned cleanup in net/ipv4/raw.c

This patch gets rid of the following gcc -W warning in net/ipv4/raw.c :

net/ipv4/raw.c:387: warning: comparison of unsigned expression < 0 is always false

Since 'len' is of type size_t it is unsigned and can thus never be <0, and 
since this is obvious from the function declaration just a few lines above 
I think it's ok to remove the pointless check for len<0.


Signed-off-by: Jesper Juhl <juhl-lkml@dif.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>