net: driver: hamradio: Fix potential unterminated string

net: driver: hamradio: Fix potential unterminated string

With W=1 the following error is reported:

In function ‘strncpy’,
    inlined from ‘hdlcdrv_ioctl’ at drivers/net/hamradio/hdlcdrv.c:600:4:
./include/linux/string.h:297:30: warning: ‘__builtin_strncpy’ specified bound 32 equals destination size [-Wstringop-truncation]
  297 | #define __underlying_strncpy __builtin_strncpy
      |                              ^
./include/linux/string.h:307:9: note: in expansion of macro ‘__underlying_strncpy’
  307 |  return __underlying_strncpy(p, q, size);

Replace strncpy with strlcpy to guarantee the string is terminated.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20201031181700.1081693-1-andrew@lunn.ch
Signed-off-by: Jakub Kicinski <kuba@kernel.org>