samples: http_server: Fix warning about integer name

When building with CONFIG_DEBUG=y, there is a build warning about the
name being truncated due to integer size is larger than MAX_NAME_LEN.
So fix MAX_NAME_LEN to be large enough to handle 10 digit integer, which
is maximum.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>