bf533-stamp, bf538f-ezkit, and cm-bf548 are very space limited.

This was introduced by:
6e0d26c0502e (net: Handle ethaddr changes as an env callback)
by enabling CONFIG_REGEX, which is too big for these boards.

This patch disables CONFIG_REGEX at the expense of working with more
than the first ethaddr.

Signed-off-by: Joe Hershberger