ibmvnic: Use kernel helpers for hex dumps

ibmvnic: Use kernel helpers for hex dumps

Previously, when the driver was printing hex dumps, the buffer was cast
to an 8 byte long and printed using string formatters. If the buffer
size was not a multiple of 8 then a read buffer overflow was possible.

Therefore, create a new ibmvnic function that loops over a buffer and
calls hex_dump_to_buffer instead.

This patch address KASAN reports like the one below:
  ibmvnic 30000003 env3: Login Buffer:
  ibmvnic 30000003 env3: 01000000af000000
  <...>
  ibmvnic 30000003 env3: 2e6d62692e736261
  ibmvnic 30000003 env3: 65050003006d6f63
  ==================================================================
  BUG: KASAN: slab-out-of-bounds in ibmvnic_login+0xacc/0xffc [ibmvnic]
  Read of size 8 at addr c0000001331a9aa8 by task ip/17681
  <...>
  Allocated by task 17681:
  <...>
  ibmvnic_login+0x2f0/0xffc [ibmvnic]
  ibmvnic_open+0x148/0x308 [ibmvnic]
  __dev_open+0x1ac/0x304
  <...>
  The buggy address is located 168 bytes inside of
                allocated 175-byte region [c0000001331a9a00, c0000001331a9aaf)
  <...>
  =================================================================
  ibmvnic 30000003 env3: 000000000033766e

Fixes: 032c5e82847a ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Reviewed-by: Dave Marquardt <davemarq@linux.ibm.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250320212951.11142-1-nnac123@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>