Changes

Fix missing include of linux/string.h

dahdi-base.c: In function 'dahdi_ioctl_get_version':
dahdi-base.c:5452:17: error: implicit declaration of function 'strncpy' [-Werror=implicit-function-declaration]
5452 |                 strncpy(vi.echo_canceller, ec_name, space);
      |                 ^~~~~~~
dahdi-base.c:96:1: note: include '<string.h>' or provide a declaration of 'strncpy'
   95 | #include "arith.h"
  +++ |+#include <string.h>

Change-Id: Id1341c146b82f0d64370a23ec07432d7055bf13e