RDMA/ionic: Use ether_addr_copy instead of memcpy

RDMA/ionic: Use ether_addr_copy instead of memcpy

eth header from ib_ud_header structure packs the mac
into 4B high and 2B low parts. But when 4B high is used
in memcpy, it sees it as overflow. However, this is safe
due to the 4B high and 2B low arrangement in the structure.
To avoid the memcpy warning, use ether_addr_copy to copy
the mac address.

In function ‘fortify_memcpy_chk’,
    inlined from ‘ionic_set_ah_attr.isra’ at drivers/infiniband/hw/ionic/ionic_controlpath.c:609:3:
./include/linux/fortify-string.h:580:25: error: call to ‘__read_overflow2_field’ declared with attribute warning: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror=attribute-warning]
  580 |                         __read_overflow2_field(q_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[6]: *** [scripts/Makefile.build:287: drivers/infiniband/hw/ionic/ionic_controlpath.o] Error 1
make[5]: *** [scripts/Makefile.build:556: drivers/infiniband/hw/ionic] Error 2
make[5]: *** Waiting for unfinished jobs....
make[4]: *** [scripts/Makefile.build:556: drivers/infiniband/hw] Error 2
make[3]: *** [scripts/Makefile.build:556: drivers/infiniband] Error 2
make[2]: *** [scripts/Makefile.build:556: drivers] Error 2
make[1]: *** [/tmp/tmp53nb1nwr/Makefile:2011: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2

Fixes: e8521822c733 ("RDMA/ionic: Register device ops for control path")
Reported-by: Leon Romanovsky <leon@kernel.org>
Closes: https://lore.kernel.org/lkml/20250918180750.GA135135@unreal/
Signed-off-by: Abhijit Gangurde <abhijit.gangurde@amd.com>
Link: https://patch.msgid.link/20250919121301.1113759-2-abhijit.gangurde@amd.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>