[SK_BUFF]: Introduce skb_copy_from_linear_data{_offset}

To clearly state the intent of copying from linear sk_buffs, _offset being a
overly long variant but interesting for the sake of saving some bytes.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/net/netrom/nr_subr.c b/net/netrom/nr_subr.c
index 07b694d..04e7d0d2 100644
--- a/net/netrom/nr_subr.c
+++ b/net/netrom/nr_subr.c
@@ -226,13 +226,13 @@
 
 	dptr = skb_put(skbn, NR_NETWORK_LEN + NR_TRANSPORT_LEN);
 
-	memcpy(dptr, skb->data + 7, AX25_ADDR_LEN);
+	skb_copy_from_linear_data_offset(skb, 7, dptr, AX25_ADDR_LEN);
 	dptr[6] &= ~AX25_CBIT;
 	dptr[6] &= ~AX25_EBIT;
 	dptr[6] |= AX25_SSSID_SPARE;
 	dptr += AX25_ADDR_LEN;
 
-	memcpy(dptr, skb->data + 0, AX25_ADDR_LEN);
+	skb_copy_from_linear_data(skb, dptr, AX25_ADDR_LEN);
 	dptr[6] &= ~AX25_CBIT;
 	dptr[6] |= AX25_EBIT;
 	dptr[6] |= AX25_SSSID_SPARE;