Tap network interface initialization in sandbox
barebox leads to segfault under Debian Buster/Sid.

The problem is that strcpy(dev, ifr.ifr_name) inside
tap_alloc() tries to alter read-only data passed
by tap_probe() and barebox receives SIGSEGV.

Nobody uses network interface name returned
by tap_alloc() so we can drop this strcpy().

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>