bitbake: main: Check bitbake server-only port is a number

bitbake: main: Check bitbake server-only port is a number

Either using the memres script or the bitbake call with --server-only
if the port is a string instead of a number then the process hangs
indefinitely causing a loop that never ends.

Add a check at the beginning for the port being a number otherwise
show an error message and exit cleanly.

[YOCTO #10397]

(Bitbake rev: 35927a98daeeb854ef5782e900206af6cd96b3d7)

Signed-off-by: Benjamin Esquivel <benjamin.esquivel@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>