P2P: Advertise IP Address Allocation only if it is enabled on GO

P2P: Advertise IP Address Allocation only if it is enabled on GO

This group capability bit was previously added unconditionally which
could result in the P2P Client assuming the functionality is available
even though the GO would always reject the request (not reply to it with
an assigned IP address) during the 4-way handshake.

Fix this by advertising the capability only if the GO configuration
allow IP address assignment to be completed.

Signed-off-by: Jouni Malinen <j@w1.fi>