vhost: fix name not null terminated

vhost: fix name not null terminated

Fix issue reported by Coverity.
Coverity ID 124556

If the buffer is treated as a null terminated string in later operations,
a buffer overflow or over-read may occur.

In vhost_set_ifname: The string buffer may not have a null terminator if
the source string's length is equal to the buffer size

Fixes: 54292e9520e0 ("vhost: support ifname for vhost-user")

Signed-off-by: Daniel Mrzyglod <danielx.t.mrzyglod@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>