Update Bolt 11 default recommendation

Author: t-bast

02-peer-protocol.md

@@ -745,7 +745,7 @@ almost arbitrary fees), `S` should be small during normal operation; although,
 given that block times are irregular, empty blocks still occur, fees may vary
 greatly, and the fees cannot be bumped on HTLC transactions, `S=12` should be
 considered a minimum. `S` is also the parameter that may vary the most under
-attack, so a higher value may be desirable when non negligible amounts are at
+attack, so a higher value may be desirable when non-negligible amounts are at
 risk. The grace period `G` can be low (1 or 2), as nodes are required to timeout
 or fulfill as soon as possible; but if `G` is too low it increases the risk of
 unnecessary channel closure due to networking delays.
@@ -767,7 +767,7 @@ There are four values that need be derived:
 4. the minimum `cltv_expiry` accepted for terminal payments: the
    worst case for the terminal node C is `2R+G+S` blocks (as, again, steps
    1-3 above don't apply). The default in [BOLT #11](11-payment-encoding.md) is
-   9, which is less conservative than the 18 that this calculation suggests.
+   18, which matches this calculation.
 
 #### Requirements
 

11-payment-encoding.md

@@ -142,7 +142,7 @@ Currently defined tagged fields are:
 * `n` (19): `data_length` 53. 33-byte public key of the payee node
 * `h` (23): `data_length` 52. 256-bit description of purpose of payment (SHA256). This is used to commit to an associated description that is over 639 bytes, but the transport mechanism for the description in that case is transport specific and not defined here.
 * `x` (6): `data_length` variable. `expiry` time in seconds (big-endian). Default is 3600 (1 hour) if not specified.
-* `c` (24): `data_length` variable. `min_final_cltv_expiry` to use for the last HTLC in the route. Default is 9 if not specified.
+* `c` (24): `data_length` variable. `min_final_cltv_expiry` to use for the last HTLC in the route. Default is 18 if not specified.
 * `f` (9): `data_length` variable, depending on version. Fallback on-chain address: for Bitcoin, this starts with a 5-bit `version` and contains a witness program or P2PKH or P2SH address.
 * `r` (3): `data_length` variable. One or more entries containing extra routing information for a private route; there may be more than one `r` field
    * `pubkey` (264 bits)