hostapd: fix anqp_3gpp_cell_net list delimiter

hostapd: fix anqp_3gpp_cell_net list delimiter

This patch fixes the list delimiter between 3GPP networks
passed to hostapd.

> list iw_anqp_3gpp_cell_net '262,001'
> list iw_anqp_3gpp_cell_net '262,002'

When passing a list of "iw_anqp_3gpp_cell_net" parameters via UCI,
hostapd would crash at startup:
> daemon.err hostapd: Line 73: Invalid anqp_3gpp_cell_net: 262,001:262,002

Using a semicolon as a delimiter, hostapd will start as expected.

Signed-off-by: Sarah Maedel <git@tbspace.de>