removes redundant vector allocations before calling sendmmsg::batch_send #8151

Job	Run time
android (ubuntu-20.04, x86_64-linux-android)	2m 19s
ios (macos-13, aarch64-apple-ios)	3m 54s
android (ubuntu-20.04, aarch64-linux-android)	2m 28s
ios (macos-13, x86_64-apple-ios)	2m 46s
android (ubuntu-20.04, i686-linux-android)	2m 19s
ios (macos-13, aarch64-apple-darwin)	3m 39s
android (ubuntu-20.04, armv7-linux-androideabi)	2m 31s
ios (macos-13, x86_64-apple-darwin)	2m 43s
error_reporting	0s
	22m 39s

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