tplink-safeloader: update soft_ver for TP-Link Archer C6 v2 (EU)

tplink-safeloader: update soft_ver for TP-Link Archer C6 v2 (EU)

The last couple of TP-Link firmware releases for Archer C6 v2 (EU)
have switched to version 1.2.x. Bump the soft_ver to "1.2.1" to
allow firmware updates from the vendor web interface.

TP-Link vendor firmware releases supported by this change:
* Archer C6(EU)_V2_200110: soft_ver:1.2.1 Build 20200110 rel.60119
* Archer C6(EU)_V2_191014: soft_ver:1.2.0 Build 20191014 rel.33289

Signed-off-by: Georgi Vlaev <georgi.vlaev@gmail.com>
(cherry picked from commit ff75bbc423eddc09f5349b63c34773b04822f171)