ANDROID: GKI: Convert CONFIG_NET_9P as GKI modules

CONFIG_NET_9P: Plan 9 resource sharing via the 9P2000 protocol.

It is being used by ARCVM for file sharing between guest and host.

Removes CONFIG_UNIX=y & CONFIG_INET=y from gki_defconfig by
savedefconfig as these boolean configs are implied to set
when CONFIG_NET_9P=m.

Note: These drivers need kernel_read() and kernel_write() to
be accessed which are not allowed on KMI symbol list; so these
drivers can not be vendor or unprotected GKI modules.

Bug: 332937984
Test: TH
Change-Id: Ie5374659f70cd73706ae874f81c215ee991dadbd
Signed-off-by: Ramji Jiyani <ramjiyani@google.com>