Add support for linking against wolfSSL provided by wolfssl-sys #82

Job	Run time
docs	4m 24s
lint	2m 26s
test (libcoap-sys, openssl, msrv)	3m 49s
test (libcoap-sys, openssl, stable)	3m 42s
test (libcoap-sys, openssl, nightly)	3m 59s
test (libcoap-sys, gnutls, msrv)	3m 0s
test (libcoap-sys, gnutls, stable)	2m 31s
test (libcoap-sys, gnutls, nightly)	2m 54s
test (libcoap-sys, tinydtls, msrv)	2m 58s
test (libcoap-sys, tinydtls, stable)	2m 46s
test (libcoap-sys, tinydtls, nightly)	2m 56s
test (libcoap-sys, mbedtls, msrv)	2m 49s
test (libcoap-sys, mbedtls, stable)	2m 46s
test (libcoap-sys, mbedtls, nightly)	3m 0s
test (libcoap-sys, wolfssl, msrv)	3m 27s
test (libcoap-sys, wolfssl, stable)	3m 13s
test (libcoap-sys, wolfssl, nightly)	3m 17s
test (libcoap-rs, openssl, msrv)	3m 51s
test (libcoap-rs, openssl, stable)	4m 4s
test (libcoap-rs, openssl, nightly)	4m 33s
test (libcoap-rs, gnutls, msrv)	2m 44s
test (libcoap-rs, gnutls, stable)	2m 50s
test (libcoap-rs, gnutls, nightly)	2m 59s
test (libcoap-rs, tinydtls, msrv)	2m 53s
test (libcoap-rs, tinydtls, stable)	2m 48s
test (libcoap-rs, tinydtls, nightly)	2m 58s
test (libcoap-rs, mbedtls, msrv)	3m 2s
test (libcoap-rs, mbedtls, stable)	2m 45s
test (libcoap-rs, mbedtls, nightly)	3m 9s
test (libcoap-rs, wolfssl, msrv)	4m 15s
test (libcoap-rs, wolfssl, stable)	3m 58s
test (libcoap-rs, wolfssl, nightly)	3m 14s
	1h 44m 0s

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