core: reset txpool on sethead

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #1394 (16205da) into master (235f2a8) will increase coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head 16205da differs from pull request most recent head b8d79e7. Consider uploading reports for the commit b8d79e7 to get more accurate results

@@            Coverage Diff             @@
##           master    #1394      +/-   ##
==========================================
+ Coverage   51.67%   51.68%   +0.01%     
==========================================
  Files         463      463              
  Lines       58364    58366       +2     
==========================================
+ Hits        30159    30169      +10     
+ Misses      25902    25900       -2     
+ Partials     2303     2297       -6     

Impacted Files	Coverage Δ
core/blockchain.go	23.07% <0.00%> (-0.05%)	⬇️
core/rawdb/chain_freezer.go	16.96% <0.00%> (-4.25%)	⬇️
core/rawdb/chain_iterator.go	58.65% <0.00%> (-3.36%)	⬇️
p2p/peer.go	74.16% <0.00%> (-1.67%)	⬇️
ctxc/peer.go	68.04% <0.00%> (-0.56%)	⬇️
p2p/simulations/http.go	69.56% <0.00%> (-0.55%)	⬇️
core/rawdb/freezer.go	42.61% <0.00%> (ø)
trie/proof.go	75.75% <0.00%> (+0.30%)	⬆️
ctxc/downloader/downloader.go	77.17% <0.00%> (+0.41%)	⬆️
ctxc/downloader/queue.go	80.46% <0.00%> (+0.46%)	⬆️
... and 5 more