security/wpa_supplicant*: ctrl_iface set sendbuf size

In order to avoid running into the default net.local.dgram.maxdgram
of 2K currently when calling sendto(2) try to set the sndbuf size to
the maximum ctrl message size.
The problem occured, e.g., when the scan_list result had enough BSSIDs
so the text output would exceed 2048 bytes.

Written by: bz
PR: 274990
Obtained from: https://reviews.freebsd.org/D42558