kernel: backport eth_addr_add()

It's required by upcoming NVMEM layout drivers.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

target/linux/ath79/patches-5.15/910-unaligned_access_hacks.patch

@@ -829,7 +829,7 @@ SVN-Revision: 35130
  		*sum = csum_fold(csum_partial(diff, sizeof(diff),
 --- a/include/linux/etherdevice.h
 +++ b/include/linux/etherdevice.h
-@@ -511,7 +511,7 @@ static inline bool is_etherdev_addr(cons
+@@ -525,7 +525,7 @@ static inline bool is_etherdev_addr(cons
   * @b: Pointer to Ethernet header
   *
   * Compare two Ethernet headers, returns 0 if equal.
@@ -838,7 +838,7 @@ SVN-Revision: 35130
   * aligned OR the platform can handle unaligned access.  This is the
   * case for all packets coming into netif_receive_skb or similar
   * entry points.
-@@ -534,11 +534,12 @@ static inline unsigned long compare_ethe
+@@ -548,11 +548,12 @@ static inline unsigned long compare_ethe
  	fold |= *(unsigned long *)(a + 6) ^ *(unsigned long *)(b + 6);
  	return fold;
  #else