ncnn: test: Add support for ELU test

[monkeyking]

*For now alpha was generated by RandomFloat(0.001f, 1000.f)

[codecov-io]

Codecov Report

Merging #1589 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1589      +/-   ##
==========================================
+ Coverage   60.88%   60.93%   +0.05%     
==========================================
  Files         341      341              
  Lines       37072    37072              
==========================================
+ Hits        22572    22591      +19     
+ Misses      14500    14481      -19

Impacted Files	Coverage Δ
src/layer/elu.cpp	94.73% <0%> (+94.73%)	⬆️
src/layer/elu.h	100% <0%> (+100%)	⬆️

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[nihui]

hi, the test case is duplicated, please remove them

such as

        || test_elu(RandomMat(6, 16))
        || test_elu(RandomMat(6, 16))

[nihui]

Thanks for your contribution !

[monkeyking]

Thanks for your contribution !

mAY i hf ur photo

[kalcohol]

Thanks for your contribution !

mAY i hf ur photo

https://twitter.com/nihui