vty: fix documentation for 'ext-rach (disable|enable)'
vty: fix documentation for 'ext-rach (disable|enable)'

Do not use 'extended' because it's not the same 11-bit Access Burst,
as it was assumed before.  Add missing docs for 'enable'/'disable'.

Change-Id: I80b5a584e554eb7cc2416017b10fee032202b372

osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx