ipv4: fix fib metrics

Alessandro Suardi reported that we could not change route metrics :

ip ro change default .... advmss 1400

This regression came with commit 9c150e82ac50 (Allocate fib metrics
dynamically). fib_metrics is no longer an array, but a pointer to an
array.

Reported-by: Alessandro Suardi <[e-mail]>
Signed-off-by: Eric Dumazet <[e-mail]>
Tested-by: Alessandro Suardi <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/fib_semantics.c

···
 		    nfi->fib_prefsrc == fi->fib_prefsrc &&
 		    nfi->fib_priority == fi->fib_priority &&
 		    memcmp(nfi->fib_metrics, fi->fib_metrics,
-			   sizeof(fi->fib_metrics)) == 0 &&
+			   sizeof(u32) * RTAX_MAX) == 0 &&
 		    ((nfi->fib_flags ^ fi->fib_flags) & ~RTNH_F_DEAD) == 0 &&
 		    (nfi->fib_nhs == 0 || nh_comp(fi, nfi) == 0))
 			return fi;