freertos-plus-tcp: Update to latest commit on main branch (#76)

pxLAN91C111_FillInterfaceDescriptor() function is implemented
in freertos-plus-tcp portable code and then used in
integration/src/network_startup.c source file without being
declared resulting in function implicit declaration error.
This was working before as FreeRTOS-Plus-TCP project previously
forced the usage of C90 standard but now the standard in not forced
thus the application's standard shall be used, in our case C99 standard
is used.

Signed-off-by: Ahmed Ismail <Ahmed.Ismail@arm.com>