Increase global ctrl_iface buffer to same size as per-interface

Increase global ctrl_iface buffer to same size as per-interface

Since the global ctrl_iface can be used with IFNAME= prefix to send
commands to be processed by per-interface code, it should have the same
(well, close to same since the prefix takes some space) limits on
command length as the per-interface ctrl_iface. Increase the buffer from
256 to 4096 to achieve this.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>