How do I apply this kernel patch to /net/ipv4/ip_gre.c?

Question

I've been googling for a while about how to do patch linux kernel but still have no clue. My intention is to do a patch to /net/ipv4/ip_gre.c . the patch is from here http://patchwork.ozlabs.org/patch/264994/

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
    index 855004f..c52fee0 100644
    --- a/net/ipv4/ip_gre.c
    +++ b/net/ipv4/ip_gre.c
    @@ -572,7 +572,7 @@  static int ipgre_header(struct sk_buff *skb, struct net_device *dev,
        if (daddr)
            memcpy(&iph->daddr, daddr, 4);
        if (iph->daddr)
    -       return t->hlen;
    +       return t->hlen + sizeof(*iph);

        return -(t->hlen + sizeof(*iph));
     }

doing patch command still no success. so i tried change the line just like decribed in the patch to the file i wanted to patch, delete the (-) and add (+) line.

does the ip_gre.c file need to be compiled again??